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Register a new userHow Massive are Massive Compact Galaxies?
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Adam Muzzin
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Using a sample of nine massive compact galaxies at z ~ 2.3 with rest-frame optical spectroscopy and comprehensive U through 8um photometry we investigate how assumptions in SED modeling change the stellar mass estimates of these galaxies, and how this affects our interpretation of their size evolution. The SEDs are fit to Tau-models with a range of metallicities, dust laws, as well as different stellar population synthesis codes. These models indicate masses equal to, or slightly smaller than our default masses. The maximum difference is 0.16 dex for each parameter considered, and only 0.18 dex for the most extreme combination of parameters. Two-component populations with a maximally old stellar population superposed with a young component provide reasonable fits to these SEDs using the models of Bruzual & Charlot (2003); however, using models with updated treatment of TP-AGB stars the fits are poorer. The two-component models predict masses that are 0.08 to 0.22 dex larger than the Tau-models. We also test the effect of a bottom-light IMF and find that it would reduce the masses of these galaxies by 0.3 dex. Considering the range of allowable masses from the Tau-models, two-component fits, and IMF, we conclude that on average these galaxies lie below the mass-size relation of galaxies in the local universe by a factor of 3-9, depending on the SED models used.
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In this paper we study a key phase in the formation of massive galaxies: the transition of star forming galaxies into massive (M_stars~10^11 Msun), compact (r_e~1 kpc) quiescent galaxies, which takes place from z~3 to z~1.5. We use HST grism redshifts and extensive photometry in all five 3D-HST/CANDELS fields, more than doubling the area used previously for such studies, and combine these data with Keck MOSFIRE and NIRSPEC spectroscopy. We first confirm that a population of massive, compact, star forming galaxies exists at z~2, using K-band spectroscopy of 25 of these objects at 2.0<z<2.5. They have a median NII/Halpha ratio of 0.6, are highly obscured with SFR(tot)/SFR(Halpha)~10, and have a large range of observed line widths. We infer from the kinematics and spatial distribution of Halpha that the galaxies have rotating disks of ionized gas that are a factor of ~2 more extended than the stellar distribution. By combining measurements of individual galaxies, we find that the kinematics are consistent with a nearly Keplerian fall-off from V_rot~500 km/s at 1 kpc to V_rot~250 km/s at 7 kpc, and that the total mass out to this radius is dominated by the dense stellar component. Next, we study the size and mass evolution of the progenitors of compact massive galaxies. Even though individual galaxies may have had complex histories with periods of compaction and mergers, we show that the population of progenitors likely followed a simple inside-out growth track in the size-mass plane of d(log r_e) ~ 0.3 d(log M_stars). This mode of growth gradually increases the stellar mass within a fixed physical radius, and galaxies quench when they reach a stellar density or velocity dispersion threshold. As shown in other studies, the mode of growth changes after quenching, as dry mergers take the galaxies on a relatively steep track in the size-mass plane.
We present results on the nature of extreme ejective feedback episodes and the physical conditions of a population of massive ($rm M_* sim 10^{11} M_{odot}$), compact starburst galaxies at z = 0.4-0.7. We use data from Keck/NIRSPEC, SDSS, Gemini/GMOS, MMT, and Magellan/MagE to measure rest-frame optical and near-IR spectra of 14 starburst galaxies with extremely high star formation rate surface densities (mean $rm Sigma_{SFR} sim 3000 ,M_{odot} yr^{-1} kpc^{-2}$) and powerful galactic outflows (maximum speeds v$_{98} sim$ 1000-3000 km s$^{-1}$). Our unique data set includes an ensemble of both emission [OII]$lambdalambda$3726,3729, H$beta$, [OIII]$lambdalambda$4959,5007, H$alpha$, [NII]$lambdalambda$6548,6583, and [SII]$lambdalambda$6716,6731) and absorption MgII$lambdalambda$2796,2803, and FeII$lambda$2586) lines that allow us to investigate the kinematics of the cool gas phase (T$sim$10$^4$ K) in the outflows. Employing a suite of line ratio diagnostic diagrams, we find that the central starbursts are characterized by high electron densities (median n$_e sim$ 530 cm$^{-3}$), high metallicity (solar or super-solar), and, on average, high ionization parameters. We show that the outflows are most likely driven by stellar feedback emerging from the extreme central starburst, rather than by an AGN. We also present multiple intriguing observational signatures suggesting that these galaxies may have substantial Lyman continuum (LyC) photon leakage, including weak [SII] nebular emission lines. Our results imply that these galaxies may be captured in a short-lived phase of extreme star formation and feedback where much of their gas is violently blown out by powerful outflows that open up channels for LyC photons to escape.
The central regions of galaxies show the presence of super massive black holes and/or very dense stellar clusters. Both objects seem to follow similar host-galaxy correlations, suggesting that they are members of the same family of Compact Massive Objects. We investigate here a huge data collection of Compact Massive Objects properties to correlate them with absolute magnitude, velocity dispersion and mass of their host galaxies.
We analyze 99 Type Ia supernovae (SNeIa) observed in $H$ band (1.6--1.8 $mu$m) and find that SNeIa are intrinsically brighter in $H$-band with increasing host galaxy stellar mass. We find that SNeIa in galaxies more massive than $10^{10.44} M_{odot}$ are brighter in $H$ than SNeIa in less massive galaxies by $0.18 pm 0.05$ mag. The same set of SNeIa observed at optical wavelengths, after width-color-luminosity corrections, exhibit a $0.17 pm 0.05$ mag offset in the Hubble residuals. Removing two significant outliers reduces the step in $H$ band to $0.10 pm 0.04$ mag but has no effect on the optical mass step size. An analysis based on information criteria supports a step function with a break at $10^{10.44}~M_{odot}$ over a constant model with and without outliers for NIR and optical residuals. Less massive galaxies preferentially host more higher-stretch SNeIa, which are intrinsically brighter and bluer. It is only after correction for width-luminosity and color-luminosity relationships that SNeIa have brighter optical Hubble residuals in more massive galaxies. Thus the finding that SNeIa are intrinsically brighter in $H$ in more massive galaxies is a significant and opposite correlation as the intrinsic optical brightness. If dust and the treatment of intrinsic color variation were the main driver of the host galaxy mass correlation, we would not expect a correlation of brighter $H$-band SNeIa in more massive galaxies. The correlation we find thus suggests that dust is not the main explanation of the observed correlation between Hubble residual and host galaxy stellar mass.
The goal of this work is to understand whether the extreme environment of compact groups can affect the distribution and abundance of faint galaxies around them. We performed an analysis of the faint galaxy population in the vicinity of compact groups and normal groups. We built a light-cone mock galaxy catalogue constructed from the Millennium Run Simulation II plus a semi-analytical model of galaxy formation. We identified a sample of compact groups in the mock catalogue as well as a control sample of normal galaxy groups and computed the projected number density profiles of faint galaxies around the first- and the second-ranked galaxies. We also compared the profiles obtained from the semi-analytical galaxies in compact groups with those obtained from observational data. In addition, we investigated whether the ranking or the luminosity of a galaxy is the most important parameter in the determination of the centre around which the clustering of faint galaxies occurs. There is no particular influence of the extreme compact group environment on the number of faint galaxies in such groups compared to control groups. When selecting normal groups with separations between the 1st and 2nd ranked galaxies similar to what is observed in compact groups, the faint galaxy projected number density profiles in compact groups and normal groups are similar in shape and height. We observed a similar behaviour of the population of faint galaxies in observations and simulations in the regions closer to the 1st and 2nd ranked galaxies. Finally, we find that the projected density of faint galaxies is higher around luminous galaxies,regardless of the ranking in the compact group. The semi-analytical approach shows that compact groups and their surroundings do not represent a hostile enough environment to make faint galaxies to behave differently than in normal groups.
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