Dynamics of galaxies at z=3.2

Team responsible: Paul van der Werf (Leiden)
Team members: Marijn Franx, Lottie van Starkenburg, Mariska Kriek

Finding chart (NOTE: target is not visible!)

How and when did the discs in spiral galaxies like the Milky Way form? This is one of the longest-standing puzzles in modern cosmology.

Two general models presently describe how disk galaxies may form. One is based on a scenario in which there is a gentle collapse of gas clouds that collide and lose angular momentum. They sink towards the centre of the potential well formed by the dark matter hole, thereby producing a disc of gas in which stars are formed. The other implies that galaxies grow through repeated mergers of smaller gas-rich galaxies. Together they first produce a spherical mass distribution at the centre and any remaining gas then settles into a disk.

Recent studies of stars in the Milky Way system and nearby spiral galaxies suggest that the discs now present in these systems formed about 10Gyr ago. This corresponds to the epoch when we observe galaxies at redshifts of about 1.5 - 2.5. Interestingly, studies of galaxies at these distances seem consistent with current ideas about when disks may have formed, and there is some evidence that most of the mass in the galaxies was also assembled at that time.

The most direct way to verify such a connection is to observe galaxies at high redshift, in order to elucidate whether their observed properties are consistent with velocity patterns of rotating disks of gas and stars.

Here we propose to observe redshifted [OIII] emission from a pair of galaxies at z~3.2. The lines have previously been detected with ISAAC and show a very large ordered velocity gradient. These are therefore ideal targets for the program proposed above and demonstrate a key SINFONI science capability.

Target list
NameRA(2000)DEC(2000)Plate-Scale(s)Bands(s)Exp.time(on source)
HDF18422:32:39.71-60:31:06.23250H+K2 h

Technical details:
We will use the 250mas scale and the H+K grating. Total needed integration time on-source will be 2hours. Here I am assuming we do not need ON_OFF mode, since most of the field will be empty. However, if ON-OFF mode is preferred, a suitable off-position is 20" S, 20" W; in that case 4 hours will be needed.

Observation setup:
Pixel scale 0.25":

DITNDITSEQUENCENumber of ExpTotal time ONTotal exp time
60024ON-OFF-OFF-ON12 ON, 12 Sky7200s14400s

NOTE: assumes ON-OFF mode needed, but see under technical details above on need for ON-OFFs

You will not be able to pick up the object in continuum, so offset from a bright star is required; a suitable star is at:
22:32:59.512 -60:31:19.10
Centre on this star, then offset 101" W, 5" N to acquire the target.

Finding chart:
This is a SOFI K-band image, field size approx 3'.
NOTE: the target is NOT VISIBLE!