Utilizing spectroscopic observations taken for the VIMOS Ultra-Deep Survey (VUDS), new observations from Keck/DEIMOS, and publicly available observations of large samples of star-forming galaxies, we report here on the relationship between the star-formation rate (SFR) and the local environment ( δ gal ) of galaxies in the early universe (2 < z < 5). Unlike what is observed at lower redshifts ( z ≲ 2), we observe a definite, nearly monotonic increase in the average SFR with increasing galaxy overdensity over more than an order of magnitude in δ gal . The robustness of this trend is quantified by accounting for both uncertainties in our measurements and galaxy populations that are either underrepresented or not present in our sample (e.g., extremely dusty star-forming and quiescent galaxies), and we find that the trend remains significant under all circumstances. This trend appears to be primarily driven by the fractional increase of galaxies in high-density environments that are more massive in their stellar content and are forming stars at a higher rate than their less massive counterparts. We find that, even after stellar mass effects are accounted for, there remains a weak but significant SFR– δ gal trend in our sample implying that additional environmentally related processes are helping to drive this trend. We also find clear evidence that the average SFR of galaxies in the densest environments increases with increasing redshift. These results lend themselves to a picture in which massive gas-rich galaxies coalesce into proto-cluster environments at z ≳ 3, interact with other galaxies or with a forming large-scale medium, subsequently using or losing most of their gas in the process, and begin to seed the nascent red sequence that is present in clusters at slightly lower redshifts.
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The Gas in Virgo’s “Red and Dead” Dwarf Elliptical Galaxies
As star-forming dwarf irregulars and faint spirals fall onto a cluster, their gas content is easily and quickly removed by ram-pressure stripping or other cluster forces. Residual signs of star formation cease within 100 Myr, and only after approximately 1 Gyr do their optical features transition to elliptical.Despite this, ALFALFA has uncovered a population of three “red and dead” dwarf ellipticals in the Virgo Cluster which still have detectable reservoirs of HI. These dwarf ellipticals are extremely gas-rich—as gas-rich as the cluster’s star-forming dwarf irregulars (Hallenbeck et al. 2012). Where does this gas come from? We consider two possibilities. First, that the gas is recently acquired, and has not yet had time to form stars. Second, that the gas is primordial, and has been disrupted from being able to form stars during the current epoch.We present deep optical (using CFHT and KPNO) and HI (Arecibo and VLA) observations of this sample to demonstrate that this gas is primordial. These observations show that all three galaxies have exponentially decreasing profiles characteristic of dwarf ellipticals and that their rotation velocities are extremely low. However, like more massive elliptical galaxies with HI, these dwarf galaxies show irregular optical morphology. For one target, VCC 190, we additionally observe an HI tail consistent with a recent interaction with the massive spiral galaxy NGC 4224.
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- Award ID(s):
- 1637339
- NSF-PAR ID:
- 10030106
- Date Published:
- Journal Name:
- American Astronomical Society ... meeting
- Volume:
- 229
- ISSN:
- 2152-887X
- Page Range / eLocation ID:
- 346.11
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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