December 2023
Abstract
Active galactic nuclei (AGN) are thought to play a key role in shaping the buildup of galaxies. If AGN influence galaxy growth, then they will reasonably impact the molecular gas reservoir first, and star formation (SF) as a consequence. Literature results concerning the gas content of high-z AGN hosts are often focused on high-luminosity AGN (log(LBol/erg/s) > 46), i.e. good candidates for driving outflows. The SUPER and KASHz surveys are sibling projects that aim at assessing AGN feedback in samples of unbiased, high-z, X-ray-selected AGN. The SUPER project recently found that significant CO depletion is present only in the most massive host galaxies (log(M*/Msun) > 11), demonstrating the importance of using unbiased samples representative of the AGN population at cosmic noon.
I will present our efforts to extend such an analysis through an expanded sample of AGN at cosmic noon, obtained by merging SUPER and KASHz targets. We carried out a comparative study of the total molecular gas content, as traced by CO, of a sizable sample of cosmic noon AGN and a matched sample of non-AGN galaxies. Applying the Bayesian framework developed by the SUPER project, we find that the properties of AGN host galaxies at cosmic noon are in general very similar to those of non-AGN galaxies, thus ruling out a strong effect of AGN feedback in this gas phase on galaxy scales. Lastly, I will report on the comparison between our observational results and the predictions of cosmological simulations.
Abstract
TolTEC, a large-format (~7000 detector) imaging polarimeter, will conduct two legacy extragalactic surveys at 1.1, 1.4 and 2.0mm at the 50m Large Millimeter Telescope. The Ultra-Deep Survey of Star-forming Galaxies (~0.8 sq.deg., r.m.s. ~0.025mJy at 1.1mm) is a confusion-limited survey which ties the entire Luminous Infrared Galaxy population from redshifts 2 to 10 directly to their optical counterparts and addresses the question of how do massive galaxies build up metals and stellar mass over cosmic time. The Large Scale Structure Survey (~40-60 sq. deg., r.m.s.~0.25 mJy at 1.1mm) probes the relationships between the spatial distribution of star forming galaxies and large scale structure and provides a detailed view of clusters and their substructure via the Sunyaev-Zeldovich (SZ) effect. We show the predictions derived from cosmologically motivated simulations for these surveys and the accessibility of the community to them.
Abstract
I discuss how ESO instruments can advance measuring the mass functions of stellar-mass black holes and extrasolar planets. The recent success of interferometric resolution of microlensed images with VLTI-GRAVITY opens up a new venue for discovering isolated stellar remnants. GRAVITY+ will be capable of discovering a large sample of black holes and studying their distributions. Microlensing is unique at finding low-mass cold planets beyond the snow line and free-floating planets. ELT AO imaging will be able to make a breakthrough in characterizing the mass function of microlensing planets.
November 2023
Abstract
Massive stars play crucial roles in shaping the physical and chemical evolution of galaxies, influencing their environment from the early protostellar phase, where powerful jets impact the surroundings, to their violent deaths as supernovae. However, observing these stars and their immediate environments directly proves challenging due to their formation within deeply embedded parental clouds. Since accretion and ejection processes are inherently linked, protostellar outflows, which can extend several parsecs, provide crucial information about the mechanisms governing massive star formation near the central engine and unveil the elusive massive protostars. There is also mounting evidence suggesting that massive protostars may accumulate mass in episodic events, indicated by the knotty structure of jets and recent accretion burst discoveries. In this talk, I will guide you through an observational journey in massive star-forming regions, focusing on the near-infrared and data from the VLT, LBT, HST, and JWST. Additionally, I will introduce a newly developed Python package called 'sedcreator,' designed specifically for fitting spectral energy distributions for massive protostars.
Abstract
A cosmological magnetic field of nG strength on Mpc length scales could be the seed magnetic field needed to explain observed few microG large-scale galactic magnetic fields. I first briefly review the observational and theoretical motivations for such a seed field, two galactic magnetic field amplification models, and some non-inflationary seed field generation scenarios. I then discuss an inflation magnetic field generation model. I conclude by mentioning possible extensions of this model as well as potentially observable consequences.
Abstract
The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is an upcoming radio interferometer array to be located at the South African Radio Astronomy Observatory (SARAO) Square Kilometre Array (SKA) site in South Africa. HIRAX is entering into the deployment phase of the initial 256-element array of 6 metre dishes each of which will be instrumented with dual-polarisation feeds operating over a frequency range of 400-800 MHz. I will present an overview of the HIRAX instrument and science goals, focusing on the planned cosmological intensity mapping survey. Through this survey of ~15,000 square degrees of the southern sky, HIRAX aims to tomographically map the distribution of large-scale structure over the redshift range of 0.775–2.55, as traced by the 21 cm emission of neutral hydrogen. Due to the presence of strong foreground signals at low frequencies, the success of this survey relies on the careful control of calibration and systematics. I will discuss the design, instrument characterisation and analysis challenges that this presents.
Abstract
In this talk I report upon our results on the intracluster medium (ICM) of two clusters at the time when first clusters start to emerge from the cosmic web, z~2. Results are derived from new, high resolution, deep SZ and X-ray data providing us with the measurement of the two most distant resolved pressure profiles. IDCSJ1426 cluster at z=1.75 has a core whose properties are not far from the final stage, while the remaining part of the cluster is experiencing a sizable gas, heat and entropy transfer. JKCS041 at z=1.80 is caught just after a major merger event as evidenced by its SZ-X-ray peak offset, its low central pressure, and its low Compton-Y parameter compared to its WL mass. Comparison with plausible descendents shows that its ICM will experience major changes at all radii.
October 2023
Abstract
For a proper understanding of the evolution of high-redshift galaxy clusters, it is necessary to consider both passive and star-forming galaxies. Because of the cost associated with spectroscopy over a large field of view, alternative searches based on candidate colors are suggested. To distinguish passive galaxies from star-forming ones, additional color constraints are required. Based on imaging of 64 high-redshift radio AGN (1 < z < 2) using Spitzer, Herschel, the Hubble Space Telescope, and other ground-based facilities, about 40 young clusters have been identified. The redshift of the clusters, which is the radio AGN, is known, and the candidate cluster galaxies have been deduced using color criteria. The presence of red overdensities (within a 250 kpc radius) confirms the cluster formation. However, the red galaxies display a wide range of colors, some of which exhibit a rest-frame UV excess. In certain clusters, there is an inner concentration of blue galaxies, indicating active star formation even at the core of the clusters. The derived number of central luminous red galaxies and the radial density profiles are comparable to those found in local clusters, indicating that some 3C clusters are already mass-rich and compact.
Abstract
High-resolution ALMA observations have opened a new window to study galaxy dynamics at z>1, using cold gas tracers such as CO, [CI], and [CII] emission lines. In this talk, I will present recent results on cold gas dynamics in high-z galaxies, focusing in particular on the ALMA TRICEPS survey of massive galaxies at z=4-5. In all the observed galaxies, the cold gas forms dynamically-cold rotation-supported disks, indicating that regular rotation is ubiquitous in massive systems up to z=5. In several cases, the galaxy rotation curve requires the presence of a central mass concentration (a stellar bulge) in addition to a pure exponential disk. Overall, the ALMA data suggest that massive galaxies must have formed and evolved surprisingly fast during the first billion years of the Universe's lifetime.
Abstract
Evolutionary scenarios predict that obscured quasars play a key role in the evolution of galaxies; however, this role has not yet been fully understood since quasar samples are typically biased against obscured systems. We select and constrain the AGN and host galaxy properties of a complete and unbiased sample of 578 infrared (IR) quasars (𝐿AGN,IR>1e45erg/s) at 𝑧<3, using spectral and photometric data from X-rays to radio wavelengths. We find that 61% IR quasars are obscured (55% are X-ray undetected) and identify fundamental differences in the average properties of obscured and unobscured quasars: 1) obscured quasars have star-formation rates ≈3 times higher, driven by a larger population of extreme starburst host galaxies, 2) obscured quasars have stronger radio emission, potentially due to the interaction of jets or winds with a higher opacity circumnuclear medium (i.e., quasar “feedback”), and 3) obscured quasars cluster significantly more strongly than their unobscured counterparts. The suppression of star formation in unobscured quasars is potentially caused by the interaction between jets or winds with the interstellar medium, which can blow out the star-forming gas. We find that many of the obscured quasars are sub-mm galaxies and show that part of the obscuration can be due to compact dusty starbursts in the most extreme cases. We will also present and show our predictions for our 4MOST IR AGN survey, which will target ~200000 obscured quasars. We will discuss the role of obscured quasars in the evolution of galaxies, and how future facilities will help to improve understanding of this topic.
Abstract
The circumgalactic medium (CGM) is a crucial component of galaxy evolution, but thus far its physical properties are highly unconstrained. As of yet, no cosmological simulation has reached convergence when it comes to constraining the cold and dense gas fraction of the CGM. Such components are also challenging to observe, as they require sub-millimeter instruments with a high sensitivity to extended and mostly diffuse emission.
We present a state-of-the-art theoretical effort at modeling the [CII]158 micron, [CI](1-0)609 micron, [CI](2-1)370 micron, CO(3-2)867micron, and [OIII]88 micron line emissions that arise from the ISM and CGM of galaxies. We use the high-resolution cosmological zoom-in simulation Ponos, which represents a typical star forming galaxy system at z = 6.5, composed of a main disc with stellar mass M_stellar = 2 *10**9 M_sol, that is undergoing a major merger. We adopt different modeling approaches based on the photoionisation code Cloudy. Our fiducial model uses radiative transfer post-processing with RamsesRT and Krome (KramsesRT) to create more realistic FUV radiation fields, which we then compare to other sub-grid modeling approaches adopted in the literature.
We find significant differences in the luminosity and in the contribution of different gas phases and galaxy components between the different modeling approaches.
[CII] is the least model-dependant gas tracer, while [CI](1-0) and CO(3-2) are very model-sensitive. In all models, we find a significant contribution to the emission of [CII] (up to ~10%) and [OIII] (up to ~20%) from the CGM. Our fiducial RT model produces a lower density, T ~ 10**4 K tail of [CII] emission that is not seen in the other more simplistic models and that resides entirely in the CGM. Notably, [CII] and [OIII] trace different regions of the CGM: [CII] arises from an accreting filament and from the tidal tails connecting the main disc and its merging satellites, while [OIII] traces a puffy halo surrounding the main disc, probably linked to supernova feedback.
We discuss our results in the context of sub-millimetric observations, highlighting the limitations of ALMA for observing the cold ISM and CGM from sources that have a large angular extent on the sky.
This project is part of the ongoing efforts at producing theoretical predictions for future submm observations with AtLAST and is funded by the AtLAST EU grant.
September 2023
Abstract
Recent advancements in distance measurement techniques have unveiled discrepancies in the estimation of the Hubble parameter between early and late Universe indicators. Additionally, non-negligible disagreements have emerged in the Hubble parameter values derived from near-Universe indicators, such as Cepheids and the Tip of the Red Giant Branch (TRGB). Thus, the establishment of new, independent, and reliable distance estimation methods provides an important sanity check.
In this context, Type II supernovae have remained an underutilized resource. Their relatively straightforward physics, combined with recent advancements in modelling techniques, make it possible to estimate precise distances without relying on the calibration ladder. Apart from describing the potential of Type II supernovae as a dependable distance measurement tool, I will also showcase it by presenting the results of two recent empirical tests:
- Internal Consistency Assessment: I will discuss the application of this method to a sample of Type II supernova siblings, aiming to assess the internal consistency of the technique (Csörnyei et al. 2023a, https://ui.adsabs.harvard.edu/abs/2023A%26A...672A.129C/abstract
- Direct Comparison with Cepheid and TRGB Distances: I will alsopresent a direct comparison between Type II supernova distance estimates and those derived from Cepheid and TRGB measurements, using the case study of Messier 51 (Csörnyei et al. 2023b, https://ui.adsabs.harvard.edu/abs/2023arXiv230513943C/abstract.
Both of these initial tests yield encouraging results, showing that obtaining a high-precision value for H0 through Type II supernovae alone is indeed possible.
Abstract
We map the emission from the intergalactic medium and circumgalactic medium based on the extremely deep MUSE observations on the Hubble Ultra Deep Field. Spanning physical scales from a few tens to hundreds of kiloparsecs, our observations uncover varying physical processes at different proximities to galaxies. Key findings include: (1) an anisotropic MgII emission within 15 kpc around z~1 galaxies provides compelling evidence for bi-polar galactic outflows. We demonstrate that these cool, metal-enriched outflows are prevalent among massive galaxies. (2) In the case of Lyα emitters within the redshift range of 3<z<4, an average blueshift in the Lyα line extending up to 70 kpc from the galaxy suggests the existence of large-scale gas inflows. (3) We have also detected extended Lyα emission reaching out to approximately 270 kpc, marking a significant advancement in our understanding of these regions. This talk will end by previewing our ongoing efforts to reproduce the observed surface brightness and kinematic characteristics of Lyα haloes through simulations.
Abstract
In this presentation, I will present the latest findings derived from the SERRA suite, a set of cosmological simulations zooming in on high-z galaxies, spanning from the Epoch of Reionization to the Cosmic High Noon. The discussion will address two particular questions: 1) Why are the super-early (z>10) galaxies identified with JWST dim in ALMA FIR observations? 2) Do cosmological simulations predict the presence of dynamically cold disk galaxies, marked by substantial rotational support, as observed with ALMA? How will JWST/NIRSpec observations enrich our understanding of these intriguing galaxies?
Abstract
With the completion of ALMA, we now have unparalleled spatial resolution at submm wavelengths, enabling detailed kinematic studies of z > 4 galaxies for the first time. In this presentation, I will show kinematic models of four galaxies at z ~ 4.5, with some of the most spatially resolved observations in [CII] using ALMA. Our findings indicate that each of these galaxies features a regularly rotating disc, and their gas velocity dispersions are significantly lower than predicted by current cosmological hydrodynamical simulations. By decomposing the rotation curves into the different mass components, we derive properties of both the dark matter halo and baryons within the inner 3 to 5 kpc. Aditionally, by analysing the velocity dispersion in the discs, we find that the gas turbulence is likely driven by the intense stellar feedback, without the need for gravitational instabilities. Furthermore, we contextualise these galaxies within the baryonic Tully-Fisher relation, exploring potential evolutionary links to local elliptical galaxies. Our findings show that cold discs can form earlier than previously thought and suggest that stellar feedback is at play to control the gas turbulence.
July 2023
Abstract
The Dark Energy Spectroscopic Instrument (DESI) is currently in its 3rd year of operation and just made public its first data release: the data from the period of Survey Validation. Located at Kitt Peak National Observatory, this multi-object spectrograph is putting together the largest 3D map of the observable universe created to date. I will give a status update on the DESI project, present the Early Data Release as well as give an overview of the early science results.
Abstract
The analysis of stellar populations is a very important part of understanding galaxy formation and evolution. While in nearby galaxies this can be done through the study of individual stars, at larger distances, discrete tracers become crucial tools that allow us to map the properties of stellar populations where individual stars cannot be resolved or detected. In this talk, I will introduce the two main types of discrete tracers, globular clusters and planetary nebulae, and I will give an overview of the ways in which we can use them to uncover the properties of halos.
Abstract
The exoplanet system around the low-mass star (0.09 solar) TRAPPIST-1 is perhaps the most iconic example of a compact, multi-planet system. The planets are found at close distances from the star (but some at moderate irradiation levels) and are all in mean motion resonances. Recently, modelling of transit timings variations and photometry have resulted in unprecedented constraints on the planets masses, compositions, and their dynamical state in terms of Laplace resonance angles. These constraints offer an opportunity to inform us how the system assembled. I will present numerical simulations that reproduce the physical and dynamical properties of the TRAPPIST planets. It is found that the latter is only possible in a formation context, that is, the present dynamical state of the TRAPPIST-1 system had already been established in its first few million years.
June 2023
Abstract
One of the key open questions in galaxy evolution is how efficiently galaxies form stars as a function of cosmic time. In order to solve this problem, it is crucial to reconstruct the star formation rate density (SFRD) to the highest possible redshifts. However, the available information at z>3 is limited and biased towards UV-luminous galaxies. One approach is to search for star-forming galaxies (SFGs) at z>3 missed by optical/NIR surveys because of dust obscuration.
In this talk, I will illustrate the potentialities of a radio selection. In particular, I will present the largest homogeneous sample, so far, of Radio-Selected NIR-Dark galaxies, that we have collected in the COSMOS field pairing the radio data from the VLA-COSMOS 3GHz Large Project to a lack of counterpart in the COSMOS2020 photometric catalogue.
I will show the properties of these galaxies, with a particular focus on what we can learn from sub-mm spectra that we collected as part of a dedicated ALMA follow-up campaign. Part of our sample has been/will be observed as part of the COSMOS-Web survey: I will also show how JWST is effectively pulling some of these sources out of darkness and helping us understand their elusive nature.
Finally, I will discuss the likely evolutionary path of these systems that can give a substantial contribution to the cosmic SFRD.
The mere existence of such heavily obscured galaxies in the first two billion years after the Big Bang opens new avenues to investigate the early phases of galaxy formation and evolution, and to understand the links between these systems and the massive galaxies which ceased their star formation at later cosmic times.
Abstract
The stellar mass – halo mass relationship is a fundamental scaling relationship connecting galaxies from dwarfs to giants to their dark matter halos. This relationship is currently key to our understanding of the complex interplay between the many modes of feedback (e.g., stellar winds, supernovae, AGN) and star formation in galaxies. However, recently a population of large half-light radius, low surface brightness ultra-diffuse galaxies (UDGs) have questioned our understanding of galaxy formation in the dwarf galaxy regime. UDGs have been found to reside in dark matter halos of widely varying mass. While many likely reside in “normal” dark matter halos for their stellar mass, some may exhibit an extreme lack of dark matter while yet others are extremely dark matter rich. In this talk, I give an overview of the current observational evidence for UDGs residing in massive dark matter halos. I place particular emphasis on my own Keck observations which have provided support for UDGs’ unexpected stellar mass – halo mass positioning and that has revealed the internal structure of their halo (i.e., core vs cusp nature). I discuss how these observations currently inform proposed formation scenarios for UDGs and show an outstanding tension of my observations with simulations of galaxy formation. I conclude with a brief discussion of the important future goals of the field.
Abstract
Despite the physical limitations of observing faraway worlds, the study of exoplanets has flourished in recent years. Yet, our insight into exoplanet atmospheres has lagged in the exoplanet boom.
Confidently resolved, minute changes in the observed spectral light allow us to trace exoplanet winds both globally and more recently with next-generation facilities in a time-resolved manner as the planet rotates. From this new 3D approach to exoplanetary studies, we can not only paint a picture of the atmospheric dynamics of these worlds but also gather insights into their formation, possibilities for moons, and more. Yet, any of these results rely heavily on our understanding of the instrument in use. I will give a quick overview of the use of ESPRESSO to study exoplanet atmospheres, its advantages, and current challenges.
Abstract
The formation of stars at low metallicities is a central problem in galaxy formation and evolution, i.e., to understand the properties of the high redshift universe. However, studies of the detailed star formation process in low metallicity environments have been limited due to large distances and the corresponding difficulty in characterizing low-mass sources. Here I will present a multi-wavelength campaign that employs the synergy of ALMA and JWST to characterize star formation processes of Sh2-284, one of the lowest metallicity proto clusters in the Galaxy.
May 2023
Abstract
Until now, direct observations of the intracluster medium (ICM) have been limited only to mature clusters in the latter three-quarters of the history of the Universe, and we have been lacking a direct view of the hot, thermalised cluster atmosphere beyond z~2, the epoch when the first massive clusters formed. Probing the thermal evolution of cosmic structures through z~2 — the epoch when intracluster gas starts to assemble and virialise, and cosmic star formation and the activity of active galactic nuclei (AGN) manifest a concurrent peak — is however crucial for exploring the link between galaxy clusters and their over-dense progenitors, as well as finding the observational fingerprint of feedback effects that regulate the later coevolution of the galaxy and intracluster/circumgalactic medium ecosystems.
In my talk, I will present our recent detection of the thermal Sunyaev-Zeldovich (SZ) effect in the direction of the protocluster complex surrounding the famous Spiderweb Galaxy (z~2.16), made possible only thanks to the superior capabilities of the Atacama Large Millimeter/Submillimeter Array (ALMA). Such identification of a nascent intracluster halo represents the unambiguous proof that we are witnessing the transition through which a sparse overdensity of galaxies turns into a massive galaxy cluster, providing a statistically meaningful confirmation of long-standing predictions from cosmological simulations, and cluster and galaxy evolution.
Abstract
I will report a CO(3-2) detection of 23 molecular clouds in the extended ultraviolet (XUV) disk of the spiral galaxy M83 with ALMA. The observed 1kpc2 region is at about 1.24 R25 from the disk center, where CO(2-1) was previously not detected. The detection and non-detection, as well as the level of star formation (SF) activity in the region, can be explained consistently if the clouds have the mass distribution common among Galactic clouds, such as Orion A -- with star-forming dense clumps embedded in thick layers of bulk molecular gas, but in a low-metallicity regime where their outer layers are CO-deficient and CO-dark. The most massive clouds appear similar to Orion A in SF activity as well as in gas mass. The common cloud mass structure also justifies the use of high-J CO transitions to trace the total gas mass of clouds, or galaxies, even in high-z universe. This study is the first demonstration that CO(3-2) is an efficient tracer of molecular clouds even in low-metallicity environments. In addition, if time allows, I will also briefly show a new high-fidelity CO(1-0) imaging of the full optical disk of M83 with ALMA 12m+7m+TP (435-point mosaic) at 40pc resolution with a mass sensitivity of 10^4Msun.
Abstract
The Jupiter Icy Moons Explorer (Juice) was successfully launched on 14 April 2023 from Guiana Space Centre by the European Space Agency (ESA). The main objectives are the characterization of Jupiter’s ocean-bearing icy moons – Ganymede, Europa and Callisto – as planetary objects and possible habitats, the exploration of Jupiter’s complex environment, and overall the study of the Jupiter system as an archetype for gas giants. The spacecraft with its 11 science instruments will arrive at Jupiter in July 2031 and finally go into orbit around Ganymede in 2034. I will give an overview on the instrumentation and mission design, and explain in more detail the magnetic sounding of Ganymede's subsurface ocean as an example key investigation.
Abstract
I will present results from 18 intermediate redshift clusters with spectra of about 3600 cluster members. This enabled us to use the location of star-forming (SF) galaxies, recently quenched galaxies (RQGs) and active galactic nuclei (AGN) in the projected velocity vs. position phase-space (phase-space diagram) to identify objects in the inner regions of the clusters. We found the metallicities of SF cluster galaxies with R<R200 to be enhanced with respect to the mass-metallicity relation of coeval field SF galaxies. Interestingly, this metallicity enhancement is limited to lower-mass satellites of the 9 clusters with a passive brightest cluster galaxy (BCG). A higher fraction of higher mass SF galaxies at R<R500 in the 9 clusters with active BCGs compared to the 9 clusters with passive BCGs is a signal for Galactic Conformity. On the other hand, much higher fractions of AGN and especially RQGs at R<R500 are found in clusters with passive BCGs in comparison to clusters with active BCGs. We conclude that strangulation is initiated in clusters with passive BCGs when SF satellite galaxies pass R200. Galaxies with higher masses which survived to be SF when traveling to R<R500 of clusters with passive BCGs suffer a rapid quenching of star formation, likely due to AGN triggered by the increasing ram pressure stripping toward the cluster center, which can compress the gas and fuel AGN; these AGN can rapidly quench and maintain quenched satellite galaxies.
The observed galactic conformity tells us that there is still an additional unknown "hidden common variable" that is affecting the quenching of both satellites and centrals. Since the current quenching mechanisms are too strong in the simulations (e.g., Magneticum Pathfinder, IllustrisTNG) compared to observations, new theoretical simulations with more realistic quenching mechanisms in clusters are needed in order to explore the reasons for the observed conformity.
April 2023
Abstract
Line-Intensity Mapping (LIM) is an observational technique that uses integrated emission lines from gas clouds to extract information about cosmology and extragalactic astrophysics. Unlike galaxy surveys, this technique samples even the sources which are not so bright and can reach very high redshifts to probe very large cosmological volumes. In order to extract valuable information from upcoming LIM surveys, we will need robust models to infer astrophysical/cosmological parameters from observed luminosities. In this talk, I will give an overview of the field, and present the framework I have been developing to contribute to LIM modeling. I generate LIM light cones fully based on cosmological hydrodynamic galaxy formation simulations, combined with thermal/radiative/chemical equilibrium photodissociation region (PDR) models to calculate the spectral line luminosities from every gas particle in the snapshots. In addition, I will show an application of this framework using the SIMBA simulations to generate CO and [CII] mock light cones.
Video
Abstract
Quasars are widely used in astrophysics to probe various environments, ranging from large-scale studies of clustering and the intergalactic medium to galactic-scale studies of the interstellar and circumgalactic media. Moreover, quasars are intriguing objects on their own and many aspects of quasar evolution and the multitude of observational phenomena are still not fully understood. One main limitation to quasar studies in general is the pre-selection for spectroscopic observations. The largest spectroscopic quasar samples to date have been selected based primarily on optical colors with in-homogeneous inclusion of multi-wavelength data to increase purity. Such identifications may lead to potential biases and can have severe consequences for foreground absorption studies. In this talk, I will highlight our efforts to obtain the first color-independent quasar sample by selecting candidate quasars purely based on astrometry from Gaia. This method allows us to select a sample of optically bright quasars with no further assumptions on the spectral shape. The talk will focus on the implications for studies of foreground absorption systems in particular the absorption systems caused by cold and molecular species (CI and H2).
Abstract
With a new generation of large etendue monitoring survey telescopes, there is a growing need for a number of real-time processing tasks that include: data processing for alert generation, annotation and classification, and reaction to those alerts deemed interesting optimizing the use of available follow-up facilities. In this talk, I will introduce an alert classification and reaction system called ALeRCE: Automatic Learning for the Rapid Classification of Events. ALeRCE has been selected as one of the official brokers for the Vera Rubin Observatory, and it is currently processing the Zwicky Transient Facility (ZTF) alert stream, providing machine learning classifications for variable stars, active galactic nuclei, SNe, and asteroids.
Then, I will give a short hands-on tutorial on how to use some of the ALeRCE tools publicly available for the astronomical community. So if you want to be notified when your favourite object(s) changes(), or discovery new candidates to any of the classes that we work with, come along and bring your laptop.
March 2023
Abstract
Dust scattering halos have been utilized to study spectral variations during eclipses, physical properties and distribution of dust grains in the interstellar medium (ISM), X-ray extinction and source distance determination using X-ray flux evolution and radial distribution of X-ray rings. We have obtained a Chandra image of dust scattering halo of 4U 1630-47 and used it together with low resolution 12CO images to place a constraint on the distance of the source in Kalemci et al. 2018. While the preferred distance of the analysis was 11.5 kpc, it was not possible to rule out an alternative distance of 4.7 kpc based on the distance to the prominent dust cloud. We recently obtained very high resolution radio images with the Atacama Pathfinder Experiment (APEX) which provided the exact distribution of molecular clouds in the region allowing us a much detailed spatial analysis of dust scattering. In this presentation we will discuss our findings including distance constraints for the source and molecular clouds.
Abstract
The Fornax galaxy cluster provides an unparalleled opportunity to investigate galaxy formation and evolution in a dense environment. Although the Fornax cluster seems relaxed, various studies have shown that the Fornax cluster still is accreting various sub-groups. Photometric studies of the central massive galaxy NGC 1399 revealed an excess of globular clusters (GCs), suggesting the accretion of GCs from nearby, interacting major galaxies like NGC 1404. Using the spectroscopic data from the Visible Multi-Object Spectrograph at the Very Large Telescope (VLT/VIMOS), we have kinematically characterized the photometrically detected GC candidates in the core of the cluster and produced the most extensive radial velocity catalogue of GCs in Fornax.
To understand the mass assembly of the Fornax cluster, we used this catalogue to perform dynamical mass modelling of NGC 1399 out to 200 kpc. We have investigated the effect of the intra-cluster GCs in mass modelling. Independent of the dark matter halo profiles used in modelling, we find that intra-cluster GCs have mild radial anisotropy, suggesting their accreted nature. In this talk, I will discuss the kinematic sub-structure of the intra-cluster GCs, marking the current Fornax cluster assembly. In addition, I will discuss the impact of the intra-cluster GCs on the cluster mass profile.
Abstract
By contrast to coronal X-ray detections, chromospheric emission measures seem to be a less biased indicator for magnetic activity among cool giant stars. We review the legacy of Mount Wilson "S-index" observations, and together with our own chromospheric activity monitoring data of bright, cool giants (obtained by the robotic telescope project TIGRE in Guanajuato, MEX) we put magnetic activity among giant stars into context with stellar evolution.
We show that
(1) despite huge -compared to the Sun- convective envelopes, activity is a common phenomenon among even very evolved cool giants.
(2) After crossing the Hertzsprung Gap, magnetic activity in stars >1.6 M-sun is initialized very strongly. Apart from a first-time convective envelope and not having suffered from magnetic braking before, these foot RGB giants have very fast rotating cores (Beck et al. 2012).
(3) During central Helium burning, giant activity suffers from magnetic braking (as the 4 Hyades K giants demonstrate), much like the cool MS stars.
(4) rising on the AGB, chromospheric emission is, surprisingly, rejuvenated.
More massive giants evolve quicker and are more active. But even Arcturus shows a modest activity and variability. Consequently, we suspect that any evolutionary activity increase coincides in the HRD with faster core contraction.
February 2023
Abstract
The enhanced sensitivity and resolution of modern radio-interferometers have started a new era for both Milky Way and extragalactic studies. However, with the dramatic improvement in sensitivity of interferometers such as ALMA observers face a fundamental challenge: the recovery of extended emission due to the lack of zero-spacing information. Overcoming this problem requires the combination of interferometric plus single-dish observations. In a recent international collaboration, our group investigated the application of state-of-the-art data combination techniques for radio-interferometers. Moreover, we designed novel quality assessment metrics to quantitively estimate the goodness of the data combination process as well as the quality of the resulting data products. Our analysis demonstrate the dramatic improvement of advance data combination techniques with respect to interferometric-alone images. During my talk I will present different performance tests when applying these techniques in both continuum and line ALMA observations.
Abstract
FS CMa stars are a subgroup of the B[e] stars. The forbidden emission lines and infrared excess are present in their spectra. This is a sign of very extended circumstellar region. While the B[e] phenomenon has been explained for other B[e] groups, the nature and evolutionary status of FS CMa stars has not been explained. Recently, we discovered very strong magnetic field in one of FS CMa stars, IRAS 17449+2320. The strength of the magnetic field modulus, about 6.2 kG, is in the order of the strongest Ap stars. The magnetic field together with other properties point to the post-merger origin of IRAS 17449+2320. It is very likely that among FS CMa stars other post-mergers are hidden.
The first results of our new N-body simulations show that more than half of mergers occurs in B-type stars. Which means that we are overlooking the most frequent channel of the mergers. This may have important consequence for the enrichment of the ISM by heavier elements. Especially important it may be in the early universe.
Abstract
General theory of Relativity, together with some of its postulates (Einstein’s Equivalence Principle and the isotropy of space) can be tested using spectroscopic observations of quasar absorption systems. This can be done by looking for (1) variations of fundamental constants and by (2) measuring the expected systematic redshift drift of the objects at cosmological distances due to the expansion of the Universe.
I will present our projects to perform these measurements using VLT/ESPRESSO observations aided by a newly developed spectral analysis tools based on Artificial Intelligence. The use of the Laser Frequency Comb on ESPRESSO all but removed the known instrumental systematic effects and the application of the AI methods improved the measurement robustness. I will also show the first observations aimed at measuring the redshift drift using the Lyman-alpha forest, jump-starting the future project planned with the Extremely Large Telescope.
Abstract
Women hold a very low portion of professorships in science, such as in chemistry, physics, mathematics, engineering and computer science. Why are women who are talented and dedicated enough to graduate from college not progressing through graduate school and ultimately earning full professorships? Where are these women going, and why do they leave their chosen field?
Much has been written about the underrepresentation of women professors in science, particularly in upper-level positions. Despite the substantial amount of high-quality data on this issue, however, myths and misunderstandings prevail. A frequent claim is that women are derailed by sex discrimination in publishing their work, obtaining grant funding and being hired. However, although these forms of discrimination have played important roles in the past, the current data show that none of these causes can explain today’s underrepresentation.
In this talk, I will review the most recent evidence showing that gender itself is no longer responsible for the current dearth of women in science. I will argue for the importance of another factor in women’s underrepresentation: the choice to become a mother. To place the role of this choice in context, I will consider its impact on women’s careers relative to the impacts of other variables that may reduce women’s participation in the sciences. I will show that recent findings indicate that the effect of children on women’s academic careers is so remarkable that it eclipses other factors in contributing to women’s underrepresentation in academic science.
Key factors that limit women today are still in need of solutions. Understanding the actual cause of women underrepresentation in academy is the first necessary step to create solutions to target the real issue.
Video
January 2023
Abstract
Extragalactic astronomy has made impressive progress in mapping gas around galaxies through both emission and absorption line studies. This can give us valuable insights into the `galactic ecosystem' and provide constraints on gas ejected from and inflowing onto galaxies. At the same time, theoretical models have improved to understand the physical processes at play. However, communications between these two worlds is often not easy and some "translation" of the parameters is required. In my talk, I will focus on Lyman alpha (Lya) emission and "down the barrel" absorption and present tools based on radiative transfer models to be able to fit observations providing physical quantities.
Specifically, I will discuss how parameters from such (simplified) geometries can be degereate and should be interpreted. Time provided, I will also show how these measurements can be combined with other probes such as the spatial variation of the Lya or other resonant lines.
Abstract
The unified scheme explains the differences between type I and II AGNs by the different orientation of an optically thick torus relative to the observer. The dynamics in such a torus was unclear due to the relative small scale of these objects. The unprecedented resolution of ALMA has recently allowed us to improve significantly the information about dynamics of clouds in the obscuring tori for some AGNs. On this ground, we present our N-body simulations of the toroidal structure of clouds moving around a supermassive black hole (SMBH). We apply ray-tracing algorithm to account for the effects of obscuration of the central engine by the clouds. As a result, we obtain the velocity and temperature maps which allow us to interpret the ALMA and VLTI observations. We also estimate the SMBH masses in the nearest Sy2 galaxies and provide an explanation of the counter-rotation of the torus in NGC 1068.
Abstract
Most galaxies comparable to or larger than the mass of the Milky Way host hot, X-ray emitting atmospheres and central radio sources. Hot atmospheres and radio jets and lobes are the ingredients of radio-mechanical active galactic nucleus (AGN) feedback. At least half of the most massive early type galaxies harbour multi-phase filamentary gas, which appears to result from the thermally unstable cooling of their hot atmospheres. We will present recent results based on radio and X-ray observations, which indicate that in massive early type galaxies the central radio sources are mostly switched on. We will show that for galaxies with thermally unstable hot atmospheres, the mechanical jet power correlates strongly with the Bondi accretion power. Further investigating the dependence of jet power on individual quantities in the Bondi formula, such as the supermassive black hole mass and the specific entropy of the gas at the Bondi radius, we find a very tight correlation between the jet power and black hole mass and, although poorly constrained, a hint of an anti-correlation between jet power and entropy. The results indicate that at least for thermally unstable systems, the jet power is set primarily by the supermassive black hole mass. The fact that we only see a strong correlation for thermally unstable atmospheres suggests that the black holes producing the jets and lobes are fed by cooling gas from the galactic atmospheres. It appears that once the atmosphere becomes thermally unstable, the cooling gas feeds the black holes in the centres of all galaxies at a similar jet-to-Bondi power ratio, possibly indicating a key universal property of black hole accretion in early-type galaxies. Importantly, since the central black hole mass of X-ray luminous early-type galaxies correlates with the total mass of the host halo, more massive systems undergoing thermally unstable cooling will naturally have larger jet powers.