SEPIA BAND 5 Science Verification Projects

SEPIA (Swedish ESO PI receiver for Apex) Band 5 is an instrument installed on APEX, the Atacama Pathfinder Experiment and offered for General ESO Proposals since Period 96. First light has been achieved in Feb 2015, followed by a successful commissioning and Science Verification (SV) phase. The SEPIA Band 5 receiver opens up new science opportunities in many fields of astronomy. This is the first time that a receiver covers the band 5 frequency range at a single-dish telescope at a dry site like Chajnantor in the Atacama desert, Chile.

Technical description

The SEPIA Band 5 is dual-sideband receiver covering the frequency range 159-211 GHz. The central frequencies of the two sidebands LSB and USB are separated by 12 GHz. Each sideband consists of two sub bands of 2.5 GHz each which overlap for the central 1 GHz, yielding a total frequency range of 4 GHz for each sideband. Both sidebands are observed in two polarizations. The receiver is connected to the XFFTS backend which provides a fixed number of 65536 channels per 2.5 GHz sub band. At 177 GHz, this corresponds to a spectral resolution of 0.065 km/s. The offered observing patters are On-Off observations, Raster maps, and On-the-fly (OTF) mapping. Data are taken in either beam-switching or position switching mode. At 177 GHz, the beam size is close to 35 arcsec.

At APEX, the atmospheric transmission at 183 GHz (water line) is better than 0.3 for PWV < 0.5 mm. This happens at about 15% of the total observing time (corresponding to ~50 days per year). At frequencies < 174 GHz and > 192 GHz, the atmospheric transmission is better than 0.8 for PWV< 2 mm. At 177 GHz and a PWV of 2 mm, 60 s and 1 h of on-source observing time yield an rms of 200 mK and 26 mK in 0.065 km/s wide channels, respectively.

The beam efficiencies of SEPIA band 5 will be published on the APEX web pages after a full analysis. From a preliminary analysis, we have determined ηmb=0.83 corresponding to a Jy/K=34 conversion factor thoughout band 5.

Scientific description

Here is a (non-exhaustive) list of science cases that can be studied with SEPIA Band 5:

  • The H2O(3_1,3 - 2_2,0) line at 183 GHz, many transitions of astrophysical important molecules are available in the SEPIA frequency range.
  • The J=2-1 lines of HCN, HNC, N2H+, HCO+, H13CO+, and HC18O+ are all covered.
  • The k-ladders of low-temperature tracers like CH3CN and CH3C2H are detectable with SEPIA.
  • Also, the CH3OH(4-3) line forest at ~193.5 GHz is accessible with this receiver.

Thus, different science objectives can be pursued with SEPIA, from galactic projects like low-and high-mass star formation, evolved stars, or solar system objects to extragalactic observations.

Science Verification Data Access and acknowledgements

The SV raw data are available from the ESO archive. The data can be requested by clicking on the programme ID number of the proposal (see below), or by using the APEX Archive query form.

We request that any publication using APEX data, including the public science verification data on these pages, adds the following acknowledgement as a footnote after the first mentioning of APEX in the body of the text: "This publication is based on data acquired with the Atacama Pathfinder Experiment (APEX). APEX is a collaboration between the Max-Planck-Institut fur Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory".

Publications resulting from SEPIA Band 5 data shall also refer to the following publication: Billade, B. et al., "Performance of the First ALMA Band 5 Production Cartridge", IEEE Trans. Terahertz Science and Technology, Vol. 2, No. 2, March 2012, pp.208-214.

Useful Links

SEPIA Band 5 Science Verification programs observed

  • 095.F-9801(A) PI: M. Galametz: Detecting the 183 GHz water maser emission in Arp 220
    Summary: Extragalactic masers are often detected in starbursts or active galactic nucleus (AGN) and enable us to shed light of the kinematics and physical conditions of their surrounding material. Water megamasers more specifically are usually detected toward AGNs. A water vapor emission at 183 GHz has been detected toward the ultra-luminuous infrared galaxy (ULIRG) Arp 220, providing us with crucial constraints on the physical conditions in the central part of the galaxy (Cernicharo et al, 2006). We aim to reproduce the observations for the H20 31,3-22,0 line and observe the HNC(2-1) line for the first time. We request 4 hours on the APEX telescope to achieve this goal. We will demonstrate the capacity of SEPIA to observe extragalactic extended water maser lines in view of a larger survey toward similar objects. The observation will also enable us to monitor the potential variation of the water maser emission in Arp 220.
    Status: Completed
    Technical setup: On-Off integration
    Total time including overheads: 6.2 hours
    Source RA(J2000) DEC(J2000) Lines targetted
    Arp220 15:34:57.1 +23:30:11 H2O, HNC(2-1),HCN(2-1),HCO+(2-1)
  • 095.F-9802(A) PI: A. Ginsburg: Density and Temperature in The Brick
    Summary: The Brick is a turbulent cloud in the CMZ that is very low in star formation but rich in complex molecular species. We propose observations of a few temperature and density sensitive lines in order to demonstrate the usability of Band 5 lines for physical characterization of warm molecular gas. The complex species we propose to observe, CH3CN, HCCCH, CH3CCH, HC3N, and CH3OH are usually seen only in hot cores and in extremely turbulent gas, e.g. in Arp 220 and NGC 253. These lines may therefore be uniquely useful for characterizing the high-pressure, highly turbulent gas that dominates ULIRG/starburst galaxies and high-redshift star-forming galaxies. The Brick is the best place to examine these lines in a non star-forming molecular region.
    Status: Completed
    Technical setup: On-Off integration
    Total time including overheads: 9.7 hours
    Source RA(J2000) DEC(J2000) Lines targetted
    Brick 1 17:46:10.3 -28:43:37.0 Line survey
    Brick 2 17:46:09.9 -28:42:43.4 Line survey
    Brick 3 17:46:07.5 -28:41:43.8 Line survey
  • 095.F-9803(A) PI: P. Andreani : Atomic Carbon emission in a Herschel-selected lensed galaxy at z=3.13
    Summary: We propose to tune the SEPA receiver at the expected frequencies of the atomic carbon CI J=2–1 and the CO(7-6) emission lines towards the lensed galaxy G12v2.43 at redshift 3.1276, which has been already observed by us with the APEX/LABOCA camera. The galaxy has been discovered by Herschel (Harris et al., 2012, ApJ 752, 152; Bussmann et al., 2013, ApJ 779, 25) and followed up observations have confirmed its nature: a star-forming galaxy at high-z with physical properties similar to submm galaxies. The detection of the CI line allows us to infer its molecular mass using an alternative to CO 1-0 line, while the CO(7-6) line in combination with CO(1-0), for which data are already available, will allow us to powerfuly probe the average thermal state of its considerable molecular gas reservoir, and the power sources that help maintain it.
    Status: Completed
    Technical setup: On-Off integration
    Total time including overheads: 6.3 hours (3.1h with tuning issues)
    Source RA(J2000) DEC(J2000) Lines targetted
    G12v2.43 11:35:26.3 -01:46:06.2 CO(7-6), CI(2-1)
  • 095.F-9804(A) PI: K. Immer: A SEPIA spectral line survey of Sgr B2(N)
    Summary: Sgr B2 is the most massive star forming region in the Milky Way, located in the Central Molecular Zone of our Galaxy. Here, the most complex organic molecules observed so far were detected for the first time. We propose to observe Sgr B2(N) with eight different tunings to cover the whole frequency range of SEPIA from 159 to 211 GHz. We will be able to test SEPIAs performance over the whole band and produce unbiased spectral line observations in a new frequency regime for one of the most interesting molecular line sources in the Galaxy. These observations will be comparable and complementary to an IRAM spectral line survey of Sgr B2(N) which covered only parts of the SEPIA frequency range.
    Status: Completed
    Technical setup: On-Off integration
    Total time including overheads: 4.3 hours
    Source RA(J2000) DEC(J2000) Lines targetted
    Sgr-B2(N) 17:47:20.0 -28:22:19.0 Line survey
  • 095.F-9805(A) PI: S. Wampfler : The H218O to H217O ratio towards the high-mass protostar G34.26+0.15
    Summary: Water is one of the key molecules in star-forming regions, playing important roles in both the physics and the chemistry. With the new SEPIA/ALMA band 5 receiver, it will readily become possible to observe H17O 3 −2 at 194 GHz simultaneously with its corresponding H18O transition at 203 GHz. The D/H 2 1,3 2,0 2 ratio in water is already widely used to investigate the origin and evolution of water in the Solar System. Based on the meteoritic record, the oxygen isotope ratios of water are a promising new tool to provide additional constraints on the history of water. Here, we propose to observe H17O and H18O in the high- 22 mass star-forming region G34.26+0.15 to demonstrate the capabilities of SEPIA for H2O isotopologue observations in this frequency band. Using the same rotational transition of both isotopologues ensures that the lines have comparable excitation, so that a H18O/H17O ratio can be derived easily. H18O was 222 previously observed in G34.26+0.15 with the IRAM 30m, so we have a sound estimate of the expected H17O intensity and the H18O line can be used to check the SEPIA calibration against the earlier IRAM results.
    Status: Completed
    Technical setup: On-Off integration
    Total time including overheads: 3.2 hours
    Source RA(J2000) DEC(J2000) Lines targetted
    G34.26+0.15 18:53:18.7 +01:14:58 H218O and H217O
  • 095.F-9806(A) PI: E. Humphreys: 183 GHz Water Maser Emission in Evolved Stars
    Summary: The proposal is for SEPIA SV observations of 183 GHz H2O maser emission towards a small sample of galactic evolved stars. The scientific value of understanding 183 GHz H2O maser emission in these sources is high, as they can be used to help trace physical conditions, dynamics and possibly magnetic fields in the circumstellar environment. The lines occur at known velocities in the stars, and the line profiles can contain narrow spikes, requiring relatively high spectral resolution observations. Previous observations have indicated that circumstellar 183 GHz emission can be very strong (peak up to hundreds of Jy), and that it is not highly variable. Additionally, with the centroid of the sidebands separated by 12 GHz and the 183 GHz line in the USB (centre of USB tuned to 183.9 GHz), six SiO maser/thermal line frequencies are covered by the LSB.
    Status: Completed
    Technical setup: On-Off integration
    Total time including overheads: 3.2 hours
    Source RA(J2000) DEC(J2000) Lines targetted
    VY-CMa 07:22:58.3 -25:46:03.2 H2O(3-2)
    VX-Sgr 18:08:04.0 -22:13:26.6 H2O(3-2)
    R-Aql 19:06:22.3 +08:13:48.0 H2O(3-2)
  • 095.F-9807(A) PI: B. Gullberg : Completing the CO ladder for a strongly lensed galaxy at z=2.5
    Summary: With ALMA in cycle 0 we have observed 26 strongly lensed dusty star forming galaxies selected from the South Pole Telescope survey. We obtained CO redshifts for 70% of the targets with an average redshift of z ∼ 3.5, significantly higher than previous spectroscopy surveys. We have started an ambitious project to extend the mid-J CO survey observed with ALMA with low-J CO observation using ATCA and high-J CO lines using APEX. The early result of these ongoing APEX programs show very promising results with 7/12 detected lines. We here propose to complement our high-J CO SHFI observations of our best covered source, SPT0125-47 at z = 2.515 with CO(6–5) observations using SEPIA band 5. This CO(6–5) transition will show the ability of SEPIA to detect broad, redshifted CO lines, and provide an essential constraint on the CO spectral line energy distribution (SLED), which has a gap between CO(3–2) and CO(7–6). The combined ATCA, ALMA, SEPIA and SHFI data on 7 transitions will allow us to study the star forming ISM by constraining the physical parameters of the molecular gas. These are essential to understand under which conditions stars are formed in actively star forming galaxies at high-z.
    Status: Completed
    Technical setup: On-Off integration
    Total time including overheads: 4.3 hours
    Source RA(J2000) DEC(J2000) Lines targetted
    SPT0125-47 01:25:07.1 -47:23:56.0 CO(6-5)
  • 095.F-9808(A) PI: S. Zahorecz: Deuterated formaldehyde from starless core to UCHII region
    Summary: We propose to observe the single and double deuterated formaldehyde lines (HDCO and D2CO) at 174 GHz with SEPIA toward two sources in different evolutionary stages: a starless core, AFGL5142-EC and an UCHII region, G5.89-0.39. HDCO and D2CO can be produced both in the gas phase and on grain surfaces. The comparison of these two sources in different evolutionary stages will not only allow us to investigate the Dfrac(H2CO) during the evolution of the massive star-forming cores but to understand the importance of surface chemistry in the production of the deuterated formaldehyde.
    Status: Completed
    Technical setup: On-Off integration
    Total time including overheads: 1.2 hours
    Source RA(J2000) DEC(J2000) Lines targetted
    G5.89-0.39 18:00:30.5 -24:04:01 HDCO 2(1,1)-2(0,2), D2CO 3(0,3)-2(0,2)
  • 095.F-9809(A) PI: T. van Kempen: Chemistry and UV radiation in N66
    Summary: Included in the accepted COSSA large program (van Kempen et al., in prep), N66 is the most active starforming region in the Small Magellanic Cloud. Harbouring upwards of 30 O-type stars and approximately 6% of the entire current-era SMC star-formation (Simon et al. 2007), it is a fantasic structure in the context of starforming regions in the SMC. The CO emission only consistutes <2% of the total SMC emission, originating from an expanding ring active star-forming clouds, bordered in the north by a, partly irradiated, colder cloud ("the plume") (Requena-Torres et al., subm., Muller and van Kempen, in prep). Due to the low (<20%) metallicity and thus lack of dust and PAHs, clouds are unable to be shielded from UV radiation, resulting in large fractions of CO-dark molecular gas. We propose to use SEPIA to observe the HCO+, HCN, HNC and N2H+ transitions at 3 di erent positions in N66 to characterize the influence UV radiation has on the molecular gas. While the absolute values will reveal molecular column densities, comparison between the position reveals the influence of the local UV eld on star formation in N66.
    Status: Completed
    Technical setup: On-Off integration
    Total time including overheads: 3.2 hours
    Source RA(J2000) DEC(J2000) Lines targetted
    N66 position 1 00:59:19.05 -72:09:12.3 HCO+, HCN and HNC
    N66 position 2 00:59:19.0 -72:11:23.0 HCO+, HCN and HNC
    N66 position 3 00:59:08.6 -72:11:08.4 HCO+, HCN and HNC