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Register a new userHST and Spitzer imaging of red and blue galaxies at z~2.5: A correlation between size and star formation activity from compact quiescent galaxies to extended star forming galaxies
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We present HST NICMOS+ACS and Spitzer IRAC+MIPS observations of 41 galaxies at 2<z<3.5 in the FIRES MS1054 field with red and blue rest-frame optical colors. About half of the galaxies are very compact (effective radii r_e < 1 kpc) at rest-frame optical wavelengths, the others are extended (1< r_e < 10 kpc). For reference, 1 kpc corresponds to 0.12 arcsec at z=2.5 in the adopted cosmology. We separate actively star forming galaxies from quiescent galaxies by modeling their rest-frame UV-NIR SEDs. The star forming galaxies span the full range of sizes, while the quiescent galaxies all have r_e<2kpc. In the redshift range where MIPS 24 micron imaging is a sensitive probe of re-radiated dust emission (z<2.5), the 24 micron fluxes confirm that the light of the small quiescent galaxies is dominated by old stars, rather than dust-enshrouded star formation or AGN activity. The inferred surface mass densities and velocity dispersions for the quiescent galaxies are very high compared to those in local galaxies. The galaxies follow a Kormendy relation (between surface brightness and size) with approximately the same slope as locally, but shifted to brighter surface brightnesses, consistent with a mean stellar formation redshift of z_f~5. This paper demonstrates a direct relation between star formation activity and size at z~2.5, and the existence of a significant population of massive, extremely dense, old stellar systems without readily identifiable counterparts in the local universe.
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We present spatially-resolved Atacama Large Millimeter/sub-millimeter Array (ALMA) 870 $mu$m dust continuum maps of six massive, compact, dusty star-forming galaxies (SFGs) at $zsim2.5$. These galaxies are selected for their small rest-frame optical sizes ($r_{rm e, F160W}sim1.6$ kpc) and high stellar-mass densities that suggest that they are direct progenitors of compact quiescent galaxies at $zsim2$. The deep observations yield high far-infrared (FIR) luminosities of L$_{rm IR}=10^{12.3-12.8}$ L$_{odot}$ and star formation rates (SFRs) of SFR$=200-700$ M$_{odot}$yr$^{-1}$, consistent with those of typical star-forming main sequence galaxies. The high-spatial resolution (FWHM$sim$0.12-0.18) ALMA and HST photometry are combined to construct deconvolved, mean radial profiles of their stellar mass and (UV+IR) SFR. We find that the dusty, nuclear IR-SFR overwhelmingly dominates the bolometric SFR up to $rsim5$ kpc, by a factor of over 100$times$ from the unobscured UV-SFR. Furthermore, the effective radius of the mean SFR profile ($r_{rm e, SFR}sim1$ kpc) is $sim$30% smaller than that of the stellar mass profile. The implied structural evolution, if such nuclear starburst last for the estimated gas depletion time of $Delta t=pm100$ Myr, is a 4$times$ increase of the stellar mass density within the central 1 kpc and a 1.6$times$ decrease of the half-mass radius. This structural evolution fully supports dissipation-driven, formation scenarios in which strong nuclear starbursts transform larger, star-forming progenitors into compact quiescent galaxies.
We study the evolution of the core (r<1 kpc) and effective (r<r_e) stellar-mass surface densities, in star-forming and quiescent galaxies. Since z=3, both populations occupy distinct, linear relations in log(Sigma_e) and log(Sigma_1) vs. log(M). These structural relations exhibit slopes and scatter that remain almost constant with time while their normalizations decline. For SFGs, the normalization declines by less than a factor of 2 from z=3, in both Sigma_e and Sigma_1. Such mild declines suggest that SFGs build dense cores by growing along these relations. We define this evolution as the structural main sequence (Sigma-MS). Quiescent galaxies follow different relations (Sigma^Q_e, Sigma^Q_1) off the Sigma-MS by having higher densities than SFGs of the same mass and redshift. The normalization of Sigma^Q_e declines by a factor of 10 since z=3, but only a factor of 2 in Sigma^Q_1. Thus, the common denominator for quiescent galaxies at all redshifts is the presence of a dense stellar core, and the formation of such cores in SFGs is the main requirement for quenching. Expressed in 2D as deviations off the SFR-MS and off Sigma^Q_1 at each redshift, the distribution of massive galaxies forms a universal, L-shaped sequence that relates two fundamental physical processes: compaction and quenching. Compaction is a process of substantial core-growth in SFGs relative to that in the Sigma-MS. This process increases the core-to-total mass and Sersic index, thereby, making compact SFGs. Quenching occurs once compact SFGs reach a maximum central density above Sigma^Q_1 > 9.5 M_sun/kpc^2. This threshold provides the most effective selection criterion to identify the star-forming progenitors of quiescent galaxies at all redshifts.
We present a measurement of the average supermassive black hole accretion rate (BHAR) as a function of star formation rate (SFR) for galaxies in the redshift range 0.25<z<0.8. We study a sample of 1,767 far-IR selected star-forming galaxies in the 9 deg^2 Bootes multiwavelength survey field. The SFR is estimated using 250 micron observations from the Herschel Space Observatory, for which the contribution from the AGN is minimal. In this sample, 121 AGNs are directly identified using X-ray or mid-IR selection criteria. We combined these detected AGNs and an X-ray stacking analysis for undetected sources to study the average BHAR for all of the star-forming galaxies in our sample. We find an almost linear relation between the average BHAR (in M_sun/year) and the SFR (in M_sun/year) for galaxies across a wide SFR range 0.85<log SFR<2.56 : log BHAR=(-3.72pm0.52)+(1.05pm0.33) log SFR. This global correlation between SFR and average BHAR is consistent with a simple picture in which SFR and AGN activity are tightly linked over galaxy evolution timescales.
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I. Y. Izotova Astronomical Observatory ofn Taras Shevchenko National University of Kyiv
, Kyiv
2018
We use the data for the Hbeta emission-line, far-ultraviolet (FUV) and mid-infrared 22 micron continuum luminosities to estimate star formation rates <SFR> averaged over the galaxy lifetime for a sample of about 14000 bursting compact star-forming galaxies (CSFGs) selected from the Data Release 12 (DR12) of the Sloan Digital Sky Survey (SDSS). The average coefficient linking <SFR> and the star formation rate SFR_0 derived from the Hbeta luminosity at zero starburst age is found to be 0.04. We compare <SFR>s with some commonly used SFRs which are derived adopting a continuous star formation during a period of ~100 Myr, and find that the latter ones are 2-3 times higher. It is shown that the relations between SFRs derived using a geometric mean of two star-formation indicators in the UV and IR ranges and reduced to zero starburst age have considerably lower dispersion compared to those with single star-formation indicators. We suggest that our relations for <SFR> determination are more appropriate for CSFGs because they take into account a proper temporal evolution of their luminosities. On the other hand, we show that commonly used SFR relations can be applied for approximate estimation within a factor of ~2 of the <SFR> averaged over the lifetime of the bursting compact galaxy.
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