arXiv subjects

Mauro Giavalisco

Publications and source records attributed to Mauro Giavalisco.

At least 127 records · Page 7Linked to original sources

arXiv2021

Where Do Obscured AGN Fit in A Galaxy's Timeline?

Many X-ray bright active galactic nuclei (AGN) are predicted to follow an extended stage of obscured black hole growth. In support of this picture we examine the X-ray undetected AGNs in the COSMOS field and compare their host galaxies with X-ray bright AGNs. We examine galaxies with M_\ast>10^{9.5}M_\odot for the presence of AGNs at redshifts $z=0.5-3$. We select AGNs in the infrared using \textit{Spitzer} and \textit{Herschel} detections and use color selection techniques to select AGNs within strongly star forming hosts. We stack \textit{Chandra} X-ray data of galaxies with an IR detection but lacking an X-ray detection to obtain soft and hard fluxes, allowing us to measure the energetics of these AGNs. We find a clear correlation between X-ray luminosity and IR AGN luminosity in the stacked galaxies. We also find that X-ray undetected AGNs all lie on the main sequence -- the tight correlation between SFR and $M_\ast$ that holds for the majority of galaxies, regardless of mass or redshift. This work demonstrates that there is a higher population of obscured AGNs than previously thought.

astro-ph.GA↗

arXiv2021

Implications of Increased Central Mass Surface Densities for the Quenching of Low-mass Galaxies

We use the Cosmic Assembly Deep Near-infrared Extragalactic Legacy Survey (CANDELS) data to study the relationship between quenching and the stellar mass surface density within the central radius of 1 kpc ($Σ_1$) of low-mass galaxies (stellar mass $M_* \lesssim 10^{9.5} M_\odot$) at $0.5 \leq z < 1.5$. Our sample is mass complete down to $\sim 10^9 M_\odot$ at $0.5 \leq z < 1.0$. We compare the mean $Σ_1$ of star-forming galaxies (SFGs) and quenched galaxies (QGs) at the same redshift and $M_*$. We find that low-mass QGs have higher $Σ_1$ than low-mass SFGs, similar to galaxies above $10^{10} M_\odot$. The difference of $Σ_1$ between QGs and SFGs increases slightly with $M_*$ at $M_* \lesssim 10^{10} M_\odot$ and decreases with $M_*$ at $M_* \gtrsim 10^{10} M_\odot$. The turnover mass is consistent with the mass where quenching mechanisms transition from internal to environmental quenching. At $0.5 \leq z < 1.0$, we find that the $Σ_1$ of galaxies increases by about 0.25 dex in the green valley (i.e., the transitioning region from star forming to fully quenched), regardless of their $M_*$. Using the observed specific star formation rate (sSFR) gradient in the literature as a constraint, we estimate that the quenching timescale (i.e., time spent in the transition) of low-mass galaxies is a few ($\sim4$) Gyrs at $0.5 \leq z < 1.0$. The mechanisms responsible for quenching need to gradually quench star formation in an outside-in way, i.e., preferentially ceasing star formation in outskirts of galaxies while maintaining their central star formation to increase $Σ_1$. An interesting and intriguing result is the similarity of the growth of $Σ_1$ in the green valley between low-mass and massive galaxies, which suggests that the role of internal processes in quenching low-mass galaxies is a question worthy of further investigation.

astro-ph.GA↗

arXiv2020

CLEAR: The Gas-Phase Metallicity Gradients of Star-Forming Galaxies at 0.6 < z < 2.6

We report on the gas-phase metallicity gradients of a sample of 264 star-forming galaxies at 0.6 < z < 2.6, measured through deep near-infrared Hubble Space Telescope slitless spectroscopy. The observations include 12-orbit depth Hubble/WFC3 G102 grism spectra taken as a part of the CANDELS Lya Emission at Reionization (CLEAR) survey, and archival WFC3 G102+G141 grism spectra overlapping the CLEAR footprint. The majority of galaxies (84%) in this sample are consistent with a zero or slightly positive metallicity gradient across the full mass range probed (8.5 < log M_*/M_sun < 10.5). We measure the intrinsic population scatter of the metallicity gradients, and show that it increases with decreasing stellar mass---consistent with previous reports in the literature, but confirmed here with a much larger sample. To understand the physical mechanisms governing this scatter, we search for correlations between the observed gradient and various stellar population properties at fixed mass. However, we find no evidence for a correlation with the galaxy properties we consider---including star-formation rates, sizes, star-formation rate surface densities, and star-formation rates per gravitational potential energy. We use the observed weakness of these correlations to provide material constraints for predicted intrinsic correlations from theoretical models.

astro-ph.GA↗

arXiv2020

Origin of Star-Forming Rings around Massive Centres in Massive Galaxies at $z\!<\!4$

Using analytic modeling and simulations, we address the origin of an abundance of star-forming, clumpy, extended gas rings about massive central bodies in massive galaxies at $z \!<\! 4$. Rings form by high-angular-momentum streams and survive in galaxies of $M_{\rm star} \!>\! 10^{9.5-10} M_\odot$ where merger-driven spin flips and supernova feedback are ineffective. The rings survive after events of compaction to central nuggets. Ring longevity was unexpected based on inward mass transport driven by torques from violent disc instability. However, evaluating the torques from a tightly wound spiral structure, we find that the timescale for transport per orbital time is long and $\propto\! δ_{\rm d}^{-3}$, with $δ_{\rm d}$ the cold-to-total mass ratio interior to the ring. A long-lived ring forms when the ring transport is slower than its replenishment by accretion and the interior depletion by SFR, both valid for $δ_{\rm d} \!<\! 0.3$. The central mass that lowers $δ_{\rm d}$ is a compaction-driven bulge and/or dark matter, aided by the lower gas fraction at $z \!<\! 4$, provided that it is not too low. The ring is Toomre unstable for clump and star formation. The high-$z$ dynamic rings are not likely to arise form secular resonances or collisions. AGN feedback is not expected to affect the rings. Mock images of simulated rings through dust indicate qualitative consistency with observed rings about bulges in massive $z\!\sim\!0.5\!-\!3$ galaxies, in $H_α$ and deep HST imaging. ALMA mock images indicate that $z\!\sim\!0.5\!-\!1$ rings should be detectable. We quote expected observable properties of rings and their central nuggets.

astro-ph.GA↗

arXiv2020

Selection of massive evolved galaxies at $3 \leq z \leq 4.5$ in the CANDELS fields

Using the CANDELS photometric catalogs for the HST/ACS and WFC3, we identified massive evolved galaxies at $3 < z < 4.5$, employing three different selection methods. We find the comoving number density of these objects to be $\sim 2 \times 10^{-5}$ and $8 \times 10^{-6}Mpc^{-3}$ after correction for completeness for two redshift bins centered at $z=3.4, 4.7$. We quantify a measure of how much confidence we should have for each candidate galaxy from different selections and what are the conservative error estimates propagated into our selection. Then we compare the evolution of the corresponding number densities and their stellar mass density with numerical simulations, semi-analytical models, and previous observational estimates, which shows slight tension at higher redshifts as the models tend to underestimate the number and mass densities. By estimating the average halo masses of the candidates ($M_h \approx 4.2, 1.9, 1.3 \times 10^{12} M_\odot$ for redshift bins centered at $z=3.4, 4.1, 4.7$), we find them to be consistent with halos that were efficient in turning baryons to stars and were relatively immune to the feedback effects and on the verge of transition into hot-mode accretion. This can suggest the relative cosmological starvation of the cold gas followed by an overconsumption phase in which the galaxy consumes the available cold gas rapidly as one of the possible drivers for the quenching of the massive evolved population at high redshift.

astro-ph.GA↗

arXiv2020

Quenching as a Contest between Galaxy Halos and their Central Black Holes

Existing models of galaxy formation have not yet explained striking correlations between structure and star-formation activity in galaxies, notably the sloped and moving boundaries that divide star-forming from quenched galaxies in key structural diagrams. This paper uses these and other relations to ``reverse-engineer'' the quenching process for central galaxies. The basic idea is that star-forming galaxies with larger radii (at a given stellar mass) have lower black-hole masses due to lower central densities. Galaxies cross into the green valley when the cumulative effective energy radiated by their black hole equals $\sim4\times$ their halo-gas binding energy. Since larger-radii galaxies have smaller black holes, one finds they must evolve to higher stellar masses in order to meet this halo-energy criterion, which explains the sloping boundaries. A possible cause of radii differences among star-forming galaxies is halo concentration. The evolutionary tracks of star-forming galaxies are nearly parallel to the green-valley boundaries, and it is mainly the sideways motions of these boundaries with cosmic time that cause galaxies to quench. BH-scaling laws for star-forming, quenched, and green-valley galaxies are different, and most BH mass growth takes place in the green valley. Implications include: the radii of star-forming galaxies are an important second parameter in shaping their black holes; black holes are connected to their halos but in different ways for star-forming, quenched, and green-valley galaxies; and the same BH-halo quenching mechanism has been in place since $z \sim 3$. We conclude with a discussion of black hole-galaxy co-evolution, the origin and interpretation of BH scaling laws.

astro-ph.GA↗

arXiv2020

CLEAR II: Evidence for Early Formation of the Most Compact Quiescent Galaxies at High Redshift

The origin of the correlations between mass, morphology, quenched fraction, and formation history in galaxies is difficult to define, primarily due to the uncertainties in galaxy star-formation histories. Star-formation histories are better constrained for higher redshift galaxies, observed closer to their formation and quenching epochs. Here we use "non-parametric" star-formation histories and a nested sampling method to derive constraints on the formation and quenching timescales of quiescent galaxies at $0.7 $10.25, where $Σ_1$ is the stellar mass within 1~pkpc (proper kpc). Quiescent galaxies with the highest stellar-mass surface density, $\logΣ_1 / (M_\odot\ \mathrm{kpc}^{-2}) > 10.25$, } show a \textit{minimum} formation redshift: all such objects in our sample have $z_{50} > 2.9$. Quiescent galaxies with lower surface density, $\log Σ_1 / (M_\odot\ \mathrm{kpc}^{-2}) = 9.5 - 10.25$, show a range of formation epochs ($z_{50} \simeq 1.5 - 8$), implying these galaxies experienced a range of formation and assembly histories. We argue that the surface density threshold $\logΣ_1/(M_\odot\ \mathrm{kpc}^{-2})>10.25$ uniquely identifies galaxies that formed in the first few Gyr after the Big Bang, and we discuss the implications this has for galaxy formation models.

astro-ph.GA↗

arXiv2020

Early forecasts of the evolution of the COVID-19 outbreaks and quantitative assessment of the effectiveness of countering measures

We discovered that the time evolution of the inverse fractional daily growth of new infections, N/dN, in the current outbreak of COVID-19 is accurately described by a universal function, namely the two-parameter Gumbel cumulative function, in all countries that we have investigated. While the two Gumbel parameters, as determined bit fits to the data, vary from country to country (and even within different regions of the same country), reflecting the diversity and efficacy of the adopted containment measures, the functional form of the evolution of N/dN appears to be universal. The result of the fit in a given region or country appears to be stable against variations of the selected time interval. This makes it possible to robustly estimate the two parameters from the data data even over relatively small time periods. In turn, this allows one to predict with large advance and well-controlled confidence levels, the time of the peak in the daily new infections, its magnitude and duration (hence the total infections), as well as the time when the daily new infections decrease to a pre-set value (e.g. less than about 2 new infections per day per million people), which can be very useful for planning the reopening of economic and social activities. We use this formalism to predict and compare these key features of the evolution of the COVID-19 disease in a number of countries and provide a quantitative assessment of the degree of success in in their efforts to countain the outbreak.

q-bio.PE↗

arXiv2019

Large Scale Structures in the CANDELS Fields: The Role of the Environment in Star Formation Activity

We present a robust method, weighted von Mises kernel density estimation, along with boundary correction to reconstruct the underlying number density field of galaxies. We apply this method to galaxies brighter than $\rm HST/F160w\le 26$ AB mag at the redshift range of $0.4\leq z \leq 5$ in the five CANDELS fields (GOODS-N, GOODS-S, EGS, UDS, and COSMOS). We then use these measurements to explore the environmental dependence of the star formation activity of galaxies. We find strong evidence of environmental quenching for massive galaxies ($\rm M \gtrsim 10^{11} \rm {M}_\odot$) out to $z\sim 3.5$ such that an over-dense environment hosts $\gtrsim 20\%$ more massive quiescent galaxies compared to an under-dense region. We also find that environmental quenching efficiency grows with stellar mass and reaches $\sim 60\%$ for massive galaxies at $z\sim 0.5$. The environmental quenching is also more efficient in comparison to the stellar mass quenching for low mass galaxies ($\rm M \lesssim 10^{10} \rm {M}_\odot$) at low and intermediate redshifts ($z\lesssim 1.2$). Our findings concur thoroughly with the "over-consumption" quenching model where the termination of cool gas accretion (cosmological starvation) happens in an over-dense environment and the galaxy starts to consume its remaining gas reservoir in depletion time. The depletion time depends on the stellar mass and could explain the evolution of environmental quenching efficiency with the stellar mass.

astro-ph.GA↗

arXiv2019

HST Imaging of the Ionizing Radiation from a Star-forming Galaxy at z = 3.794

We report on the HST detection of the Lyman-continuum (LyC) radiation emitted by a galaxy at redshift z=3.794, dubbed Ion1 (Vanzella et al. 2012). The LyC from Ion1 is detected at rest-frame wavelength 820$\sim$890 Åwith HST WFC3/UVIS in the F410M band ($m_{410}=27.60\pm0.36$ magnitude (AB), peak SNR = 4.17 in a circular aperture with radius r = 0.12'') and at 700$\sim$830 Åwith the VLT/VIMOS in the U-band ($m_U = 27.84\pm0.19$ magnitude (AB), peak SNR = 6.7 with a r = 0.6'' aperture). A 20-hr VLT/VIMOS spectrum shows low- and high-ionization interstellar metal absorption lines, the P-Cygni profile of CIV and Ly$α$ in absorption. The latter spectral feature differs from what observed in known LyC emitters, which show strong Ly$α$ emission. An HST far-UV color map reveals that the LyC emission escapes from a region of the galaxy that is bluer than the rest, presumably because of lower dust obscuration. The F410M image shows that the centroid of the LyC emission is offset from the centroid of the non-ionizing UV emission by 0.12''$\pm$0.03'', corresponding to 0.85$\pm$0.21 kpc (physical), and that its morphology is likely moderately resolved. These morphological characteristics favor a scenario where the LyC photons produced by massive stars escape from low HI column-density "cavities" in the ISM, possibly carved by stellar winds and/or supernova. We also collect the VIMOS U-band images of a sample of 107 Lyman-break galaxies with spectroscopic redshifts at $3.40<z<3.95$, i.e. sampling the LyC, and stack them with inverse-variance weights. No LyC emission is detected in the stacked image, resulting in a 32.5 magnitude (AB) flux limit (1$σ$) and an upper limit of absolute LyC escape fraction $f_{esc}^{abs} < 0.63\%$. LyC emitters like Ion1 are very likely at the bright-end of the LyC luminosity function.

astro-ph.GA↗

arXiv2019

The CANDELS/SHARDS multi-wavelength catalog in GOODS-N: Photometry, Photometric Redshifts, Stellar Masses, Emission line fluxes and Star Formation Rates

We present a WFC3 F160W ($H$-band) selected catalog in the CANDELS/GOODS-N field containing photometry from the ultraviolet (UV) to the far-infrared (IR), photometric redshifts and stellar parameters derived from the analysis of the multi-wavelength data. The catalog contains 35,445 sources over the 171 arcmin$^{2}$ of the CANDELS F160W mosaic. The 5$σ$ detection limits (within an aperture of radius 0\farcs17) of the mosaic range between $H=27.8$, 28.2 and 28.7 in the wide, intermediate and deep regions, that span approximately 50\%, 15\% and 35\% of the total area. The multi-wavelength photometry includes broad-band data from UV (U band from KPNO and LBC), optical (HST/ACS F435W, F606W, F775W, F814W, and F850LP), near-to-mid IR (HST/WFC3 F105W, F125W, F140W and F160W, Subaru/MOIRCS Ks, CFHT/Megacam K, and \spitzer/IRAC 3.6, 4.5, 5.8, 8.0 $μ$m) and far IR (\spitzer/MIPS 24$μ$m, HERSCHEL/PACS 100 and 160$μ$m, SPIRE 250, 350 and 500$μ$m) observations. In addition, the catalog also includes optical medium-band data (R$\sim50$) in 25 consecutive bands, $λ=500$ to 950~nm, from the SHARDS survey and WFC3 IR spectroscopic observations with the G102 and G141 grisms (R$\sim210$ and 130). The use of higher spectral resolution data to estimate photometric redshifts provides very high, and nearly uniform, precision from $z=0-2.5$. The comparison to 1,485 good quality spectroscopic redshifts up to $z\sim3$ yields $Δz$/(1+$z_{\rm spec}$)$=$0.0032 and an outlier fraction of $η=$4.3\%. In addition to the multi-band photometry, we release added-value catalogs with emission line fluxes, stellar masses, dust attenuations, UV- and IR- based star formation rates and rest-frame colors.

astro-ph.GA↗

arXiv2019

Can intrinsic alignments of elongated low-mass galaxies be used to map the cosmic web at high redshift?

Hubble Space Telescope observations show that low-mass ($M_*=10^9-10^{10}M_{\odot}$) galaxies at high redshift ($z=1.0-2.5$) tend to be elongated (prolate) rather than disky (oblate) or spheroidal. This is explained in zoom-in cosmological hydrodynamical simulations by the fact that these galaxies are forming in cosmic web filaments where accretion happens preferentially along the direction of elongation. We ask whether the elongated morphology of these galaxies allows them to be used as effective tracers of cosmic web filaments at high redshift via their intrinsic alignments. Using mock lightcones and spectroscopically-confirmed galaxy pairs from the CANDELS survey, we test two types of alignments: (1) between the galaxy major axis and the direction to nearby galaxies of any mass, and (2) between the major axes of nearby pairs of low-mass, likely prolate, galaxies. The mock lightcones predict strong signals in 3D real space, 3D redshift space, and 2D projected redshift space for both types of alignments (assuming prolate galaxy orientations are the same as those of their host prolate halos), but we do not detect significant alignment signals in CANDELS observations. However, we show that spectroscopic redshifts have been obtained for only a small fraction of highly elongated galaxies, and accounting for spectroscopic incompleteness and redshift errors significantly degrades the 2D mock signal. This may partly explain the alignment discrepancy and highlights one of several avenues for future work.

astro-ph.GA↗

arXiv2019

Another Servicing Mission to Extend Hubble Space Telescope's Science past the Next Decade

The Hubble Space Telescope has produced astonishing science over the past thirty years. Hubble's productivity can continue to soar for years to come provided some worn out components get upgraded. While powerful new ground-based and space telescopes are expected to come online over the next decade, none of them will have the UV capabilities that make Hubble a unique observatory. Without Hubble, progress in UV and blue optical astrophysics will be halted. Observations at these wavelengths are key for a range of unresolved astrophysics questions, ranging from the characterization of solar system planets to understanding interaction of galaxies with the intergalactic medium and the formation history of the universe. Hubble will remain our only source of high-angular resolution UV imaging and high-sensitivity UV spectroscopy for the next two decades, offering the ability for continued unique science and maximizing the science return from complementary observatories. Therefore, we recommend that NASA, ESA, and the private sector study the scientific merit, technical feasibility, and risk of a new servicing mission to Hubble to boost its orbit, fix aging components, and expand its instrumentation. Doing so would: 1) keep Hubble on its path to reach its unmet full potential, 2) extend the mission's lifetime past the next decade, which will maximize the synergy of Hubble with other upcoming facilities, and 3) enable and enhance the continuation of scientific discoveries in UV and optical astrophysics.

astro-ph.IM↗

arXiv2019

Nature of Faint Radio Sources in GOODS-North and GOODS-South Fields - I. Spectral Index and Radio-FIR Correlation

We present the first results from the deep and wide 5 GHz radio observations of the Great Observatories Origins Deep Survey (GOODS)-North ($σ=3.5 \; μJy \; beam^{-1}$, synthesized beam size $θ=$ 1.47 arcsec $\times$ 1.42 arcsec, and 52 sources over 109 arcmin$^{2}$) and GOODS-South ($σ=3.0 \; μJy \; beam^{-1}$, $θ=$0.98 arcsec $\times$ 0.45 arcsec, and 88 sources over 190 arcmin$^{2}$) fields using the Karl G. Jansky Very Large Array. We derive radio spectral indices α between 1.4 and 5 GHz using the beam-matched images and show that the overall spectral index distribution is broad even when the measured noise and flux bias are considered. We also find a clustering of faint radio sources around $α=0.8$, but only within $S_{5GHz} < 150 \; μJy$. We demonstrate that the correct radio spectral index is important for deriving accurate rest frame radio power and analyzing the radio-FIR correlation, and adopting a single value of $α=0.8$ leads to a significant scatter and a strong bias in the analysis of the radio-FIR correlation, resulting from the broad and asymmetric spectral index distribution. When characterized by specific star formation rates, the starburst population (58%) dominates the 5 GHz radio source population, and the quiescent galaxy population (30%) follows a distinct trend in spectral index distribution and the radio-FIR correlation. Lastly, we offer suggestions on sensitivity and angular resolution for future ultra-deep surveys designed to trace the cosmic history of star formation and AGN activity using radio continuum as a probe.

astro-ph.GA↗

arXiv2019

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.

astro-ph.GA↗

arXiv2018

CLEAR I: Ages and Metallicities of Quiescent Galaxies at $\mathbf{1.0 < z < 1.8}$ Derived from Deep Hubble Space Telescope Grism Data

We use deep \textit{Hubble Space Telescope} spectroscopy to constrain the metallicities and (\editone{light-weighted}) ages of massive ($\log M_\ast/M_\odot\gtrsim10$) galaxies selected to have quiescent stellar populations at $1.0 68$\% of their stellar mass by a redshift of $z>2$}. The posteriors give metallicities of \editone{$Z_{z\sim1.1}=1.16 \pm 0.29$~$Z_\odot$, $Z_{z\sim1.2}=1.05 \pm 0.34$~$Z_\odot$, $Z_{z\sim1.3}=1.00 \pm 0.31$~$Z_\odot$, and $Z_{z\sim1.6}=0.95 \pm 0.39$~$Z_\odot$}. This is evidence that massive galaxies had enriched rapidly to approximately Solar metallicities as early as $z\sim3$.

astro-ph.GA↗

arXiv2018

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 θ< 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.

astro-ph.GA↗

arXiv2018

Demographics of Star-forming Galaxies since $z\sim2.5$. I. The $UVJ$ Diagram in CANDELS

This is the first in a series of papers examining the demographics of star-forming galaxies at $0.2<z<2.5$ in CANDELS. We study 9,100 galaxies from GOODS-S and UDS having published values of redshifts, masses, star-formation rates (SFRs), and dust attenuation ($A_V$) derived from UV-optical SED fitting. In agreement with previous works, we find that the $UVJ$ colors of a galaxy are closely correlated with its specific star-formation rate (SSFR) and $A_V$. We define rotated $UVJ$ coordinate axes, termed $S_\mathrm{SED}$ and $C_\mathrm{SED}$, that are parallel and perpendicular to the star-forming sequence and derive a quantitative calibration that predicts SSFR from $C_\mathrm{SED}$ with an accuracy of ~0.2 dex. SFRs from UV-optical fitting and from UV+IR values based on Spitzer/MIPS 24 $μ\mathrm{m}$ agree well overall, but systematic differences of order 0.2 dex exist at high and low redshifts. A novel plotting scheme conveys the evolution of multiple galaxy properties simultaneously, and dust growth, as well as star-formation decline and quenching, exhibit "mass-accelerated evolution" ("downsizing"). A population of transition galaxies below the star-forming main sequence is identified. These objects are located between star-forming and quiescent galaxies in $UVJ$ space and have lower $A_V$ and smaller radii than galaxies on the main sequence. Their properties are consistent with their being in transit between the two regions. The relative numbers of quenched, transition, and star-forming galaxies are given as a function of mass and redshift.

astro-ph.GA↗