Evidence of Environmental Quenching at Redshift z ~ 2

We report evidence of environmental quenching among galaxies at redshift ~ 2, namely the probability that a galaxy quenches its star formation activity is enhanced in the regions of space in proximity of other quenched, more massive galaxies. The effect is observed as strong clustering of quiescent galaxies around quiescent galaxies on angular scales \theta < 20 arcsec, corresponding to a proper(comoving) scale of 168 (502) kpc at z = 2. The effect is observed only for quiescent galaxies around other quiescent galaxies; the probability to find star-forming galaxies around quiescent or around star-forming ones is consistent with the clustering strength of galaxies of the same mass and at the same redshift, as observed in dedicated studies of galaxy clustering. The effect is mass dependent in the sense that the quenching probability is stronger for galaxies of smaller mass ($\rm{M_*<10^{10} Msun}$) than for more massive ones, i.e. it follows the opposite trend with mass relative to gravitational galaxy clustering. The spatial scale where the effect is observed suggests these environments are massive halos, in which case the observed effect would likely be satellite quenching. The effect is also redshift dependent in that the clustering strength of quiescent galaxies around other quiescent galaxies at z = 1.6 is ~ 1.7 times larger than that of the galaxies with the same stellar mass at z = 2.6. This redshift dependence allows for a crude estimate of the time scale of environmental quenching of low-mass galaxies, which is in the range 1.5 - 4 Gyr, in broad agreement with other estimates and with our ideas on satellite quenching.Comment: 12 pages, 9 figures, Accepted for publication in Ap

Kpc-scale Properties of Emission-line Galaxies

We perform a detailed study of the resolved properties of emission-line galaxies at kpc-scale to investigate how small-scale and global properties of galaxies are related. 119 galaxies with high-resolution Keck/DEIMOS spectra are selected to cover a wide range in morphologies over the redshift range 0.2<z<1.3. Using the HST/ACS and HST/WFC3 imaging data taken as a part of the CANDELS project, for each galaxy we perform SED fitting per resolution element, producing resolved rest-frame U-V color, stellar mass, star formation rate, age and extinction maps. We develop a technique to identify blue and red "regions" within individual galaxies, using their rest-frame color maps. As expected, for any given galaxy, the red regions are found to have higher stellar mass surface densities and older ages compared to the blue regions. Furthermore, we quantify the spatial distribution of red and blue regions with respect to both redshift and stellar mass, finding that the stronger concentration of red regions toward the centers of galaxies is not a significant function of either redshift or stellar mass. We find that the "main sequence" of star forming galaxies exists among both red and blue regions inside galaxies, with the median of blue regions forming a tighter relation with a slope of 1.1+/-0.1 and a scatter of ~0.2 dex compared to red regions with a slope of 1.3+/-0.1 and a scatter of ~0.6 dex. The blue regions show higher specific Star Formation Rates (sSFR) than their red counterparts with the sSFR decreasing since z~1, driver primarily by the stellar mass surface densities rather than the SFRs at a giver resolution element.Comment: 17 pages, 17 figures, Submitted to the Ap

Star Formation and Clumps in Cosmological Galaxy Simulations with Radiation Pressure Feedback

Cosmological simulations of galaxies have typically produced too many stars at early times. We study the global and morphological effects of radiation pressure (RP) in eight pairs of high-resolution cosmological galaxy formation simulations. We find that the additional feedback suppresses star formation globally by a factor of ~2. Despite this reduction, the simulations still overproduce stars by a factor of ~2 with respect to the predictions provided by abundance matching methods for halos more massive than 5E11 Msun/h (Behroozi, Wechsler & Conroy 2013). We also study the morphological impact of radiation pressure on our simulations. In simulations with RP the average number of low mass clumps falls dramatically. Only clumps with stellar masses Mclump/Mdisk <= 5% are impacted by the inclusion of RP, and RP and no-RP clump counts above this range are comparable. The inclusion of RP depresses the contrast ratios of clumps by factors of a few for clump masses less than 5% of the disk masses. For more massive clumps, the differences between and RP and no-RP simulations diminish. We note however, that the simulations analyzed have disk stellar masses below about 2E10 Msun/h. By creating mock Hubble Space Telescope observations we find that the number of clumps is slightly reduced in simulations with RP. However, since massive clumps survive the inclusion of RP and are found in our mock observations, we do not find a disagreement between simulations of our clumpy galaxies and observations of clumpy galaxies. We demonstrate that clumps found in any single gas, stellar, or mock observation image are not necessarily clumps found in another map, and that there are few clumps common to multiple maps.Comment: 13 pages, 6 figures, submitted to MNRA

No evidence for feedback: Unexceptional Low-ionization winds in Host galaxies of Low Luminosity Active Galactic Nuclei at Redshift z ~1

We study winds in 12 X-ray AGN host galaxies at z ~ 1. We find, using the low-ionization Fe II 2586 absorption in the stacked spectra, that the probability distribution function (PDF) of the centroid velocity shift in AGN has a median, 16th and 84th percentiles of (-87, -251, +86) km/s respectively. The PDF of the velocity dispersion in AGN has a median, 84th and 16th percentile of (139, 253, 52) km/s respectively. The centroid velocity and the velocity dispersions are obtained from a two component (ISM+wind) absorption line model. The equivalent width PDF of the outflow in AGN has median, 84th and 16th percentiles of (0.4, 0.8, 0.1) Angstrom. There is a strong ISM component in Fe II 2586 absorption with (1.2, 1.5, 0.8) Angstrom, implying presence of substantial amount cold gas in the host galaxies. For comparison, star-forming and X-ray undetected galaxies at a similar redshift, matched roughly in stellar mass and galaxy inclination, have a centroid velocity PDF with percentiles of (-74, -258, +90) km/s, and a velocity dispersion PDF percentiles of (150, 259, 57) km/s. Thus, winds in the AGN are similar to star-formation-driven winds, and are too weak to escape and expel substantial cool gas from galaxies. Our sample doubles the previous sample of AGN studied at z ~ 0.5 and extends the analysis to z ~ 1. A joint reanalysis of the z ~ 0.5 AGN sample and our sample yields consistent results to the measurements above.Comment: 24 pages, 11 figures, accepted in Ap

The Neon Gap: Probing Ionization with Dwarf Galaxies at z~1

We present measurements of [NeIII]{\lambda}3869 emission in z~1 low-mass galaxies taken from the Keck/DEIMOS spectroscopic surveys HALO7D and DEEPWinds. We identify 167 individual galaxies with significant [NeIII] emission lines, including 112 "dwarf" galaxies with log(M_{\star}/M_{\odot}) < 9.5, with 0.3 < z < 1.4. We also measure [NeIII] emission from composite spectra derived from all [OII]{\lambda}{\lambda}3727,3729 line emitters in this range. This provides a unique sample of [NeIII]-emitters in the gap between well-studied emitters at z = 0 and 2 < z < 3. To study evolution in ionization conditions in the ISM over this time, we analyze the log([NeIII]{\lambda}3869/[OII]{\lambda}{\lambda}3727,3729) ratio (Ne3O2) as a function of the stellar mass and of the log([OIII]{\lambda}{\lambda}4959,5007/[OII]{\lambda}{\lambda}3727,3729) ratio (O32). We find that the typical star-forming dwarf galaxy at this redshift, as measured from the composite spectra, shares the Ne3O2-M_{\star} relation with local galaxies, but have higher O32 at given Ne3O2. This finding implies that the ionization and metallicity characteristics of the z~1 dwarf population do not evolve substantially from z~1 to z=0, suggesting that the known evolution in those parameter from z~2 has largely taken place by z~1. Individual [NeIII]-detected galaxies have emission characteristics situated between local and z~2 galaxies, with elevated Ne3O2 and O32 emission potentially explained by variations in stellar and nebular metallicity. We also compare our dwarf sample to similarly low-mass z > 7 galaxies identified in JWST Early Release Observations, finding four HALO7D dwarfs with similar size, metallicity, and star formation properties.Comment: Accepted to ApJL, 16.01.202

The Role of Bulge Formation in the Homogenization of Stellar Populations at z∼2z\sim2 as revealed by Internal Color Dispersion in CANDELS

We use data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey to study how the spatial variation in the stellar populations of galaxies relate to the formation of galaxies at $1.5 < z < 3.5$. We use the Internal Color Dispersion (ICD), measured between the rest-frame UV and optical bands, which is sensitive to age (and dust attenuation) variations in stellar populations. The ICD shows a relation with the stellar masses and morphologies of the galaxies. Galaxies with the largest variation in their stellar populations as evidenced by high ICD have disk-dominated morphologies (with S\'{e}rsic indexes $< 2$) and stellar masses between $10 < \mathrm{Log~M/ M_\odot}< 11$. There is a marked decrease in the ICD as the stellar mass and/or the S\'ersic index increases. By studying the relations between the ICD and other galaxy properties including sizes, total colors, star-formation rate, and dust attenuation, we conclude that the largest variations in stellar populations occur in galaxies where the light from newly, high star-forming clumps contrasts older stellar disk populations. This phase reaches a peak for galaxies only with a specific stellar mass range, $10 < \mathrm{Log~M/ M_\odot} < 11$, and prior to the formation of a substantial bulge/spheroid. In contrast, galaxies at higher or lower stellar masses, and/or higher S\'{e}rsic index ($n > 2$) show reduced ICD values, implying a greater homogeneity of their stellar populations. This indicates that if a galaxy is to have both a quiescent bulge along with a star forming disk, typical of Hubble Sequence galaxies, this is most common for stellar masses $10 < \mathrm{Log~M/M_\odot} < 11$ and when the bulge component remains relatively small ($n<2$).Comment: 15 pages, 14 figure

Evolution of the Gas Mass Fraction of Progenitors to Today's Massive Galaxies: ALMA Observations in the CANDELS GOODS-S Field

We present an ALMA survey of dust continuum emission in a sample of 70 galaxies in the redshift range z=2-5 selected from the CANDELS GOODS-S field. Multi-Epoch Abundance Matching (MEAM) is used to define potential progenitors of a z = 0 galaxy of stellar mass 1.5 10^11 M_sun. Gas masses are derived from the 850um luminosity. Ancillary data from the CANDELS GOODS-S survey are used to derive the gas mass fractions. The results at z<=3 are mostly in accord with expectations: The detection rates are 75% for the z=2 redshift bin, 50% for the z=3 bin and 0% for z>=4. The average gas mass fraction for the detected z=2 galaxies is f_gas = 0.55+/-0.12 and f_gas = 0.62+/-0.15 for the z=3 sample. This agrees with expectations for galaxies on the star-forming main sequence, and shows that gas fractions have decreased at a roughly constant rate from z=3 to z=0. Stacked images of the galaxies not detected with ALMA give upper limits to f_gas of <0.08 and <0.15, for the z=2 and z=3 redshift bins. None of our galaxies in the z=4 and z=5 sample are detected and the upper limit from stacked images, corrected for low metallicity, is f_gas<0.66. We do not think that lower gas-phase metallicities can entirely explain the lower dust luminosities. We briefly consider the possibility of accretion of very low-metallicity gas to explain the absence of detectable dust emission in our galaxies at z>4.Comment: Accepted for publication in the Astrophysical Journal. 33 pages; 11 figure

Constraining The Assembly Of Normal And Compact Passively Evolving Galaxies From Redshift z=3 To The Present With CANDELS

We study the evolution of the number density, as a function of the size, of passive early-type galaxies with a wide range of stellar masses 10^10<M*/Msun<10^11.5) from z~3 to z~1, exploiting the unique dataset available in the GOODS-South field, including the recently obtained WFC3 images as a part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). In particular, we select a sample of 107 massive (M*>10^10 M_sun), passive (SSFR<10^-2 Gyr^-1) and morphologically spheroidal galaxies at 1.2<z<3, taking advantage of the panchromatic dataset available for GOODS, including VLT, CFHT, Spitzer, Chandra and HST ACS+WFC3 data. We find that at 1<z<3 the passively evolving early-type galaxies are the reddest and most massive objects in the Universe, and we prove that a correlation between mass, morphology, color and star-formation activity is already in place at that epoch. We measure a significant evolution in the mass-size relation of passive early-type galaxies (ETGs) from z~3 to z~1, with galaxies growing on average by a factor of 2 in size in a 3 Gyr timescale only. We witness also an increase in the number density of passive ETGs of 50 times over the same time interval. We find that the first ETGs to form at z>2 are all compact or ultra-compact, while normal sized ETGs (meaning ETGs with sizes comparable to those of local counterparts of the same mass) are the most common ETGs only at z<1. The increase of the average size of ETGs at 0<z<1 is primarily driven by the appearance of new large ETGs rather than by the size increase of individual galaxies.Comment: 9 pages, 5 figures, submitted to Ap