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Title: VLT/X-SHOOTER NEAR-INFRARED SPECTROSCOPY AND HST IMAGING OF GRAVITATIONALLY LENSED z ∼ 2 COMPACT QUIESCENT GALAXIES

Abstract

Quiescent massive galaxies at z ∼ 2 are thought to be the progenitors of present-day massive ellipticals. Observations revealed them to be extraordinarily compact. Until now, the determination of stellar ages, star formation rates, and dust properties via spectroscopic measurements has been feasible only for the most luminous and massive specimens (∼3 × M*). Here we present a spectroscopic study of two near-infrared-selected galaxies that are close to the characteristic stellar mass M* (∼0.9 × M* and ∼1.3 × M*) and whose observed brightness has been boosted by the gravitational lensing effect. We measure the redshifts of the two galaxies to be z = 1.71 ± 0.02 and z = 2.15 ± 0.01. By fitting stellar population synthesis models to their spectrophotometric spectral energy distributions we determine their ages to be 2.4{sup +0.8}{sub -0.6} Gyr and 1.7 ± 0.3 Gyr, respectively, which implies that the two galaxies have higher mass-to-light ratios than most quiescent z ∼ 2 galaxies in other studies. We find no direct evidence for active star formation or active galactic nucleus activity in either of the two galaxies, based on the non-detection of emission lines. Based on the derived redshifts and stellar ages we estimate the formationmore » redshifts to be z=4.3{sup +3.4}{sub -1.2} and z=4.3{sup +1.0}{sub -0.6}, respectively. We use the increased spatial resolution due to the gravitational lensing to derive constraints on the morphology. Fitting Sérsic profiles to the de-lensed images of the two galaxies confirms their compactness, with one of them being spheroid-like and the other providing the first confirmation of a passive lenticular galaxy at a spectroscopically derived redshift of z ∼ 2.« less

Authors:
; ; ; ;  [1];  [2];  [3]
  1. Dark Cosmology Centre, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark)
  2. Centre de Recherche Astronomique de Lyon, Université Lyon 1, 9 Avenue Charles Andre, F-69230 Saint Genis Laval (France)
  3. Department of Physics and Astronomy, Tufts University, Medford, MA 06520 (United States)
Publication Date:
OSTI Identifier:
22270654
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 777; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTROSCOPY; ASTRONOMY; ASTROPHYSICS; BRIGHTNESS; COSMIC DUST; ENERGY SPECTRA; GALAXIES; GRAVITATIONAL LENSES; INFRARED SPECTRA; LIMITING VALUES; MASS; RED SHIFT; SPATIAL RESOLUTION; SPECTROPHOTOMETRY; STARS; VISIBLE RADIATION

Citation Formats

Geier, S., Man, A. W. S., Krühler, T., Toft, S., Fynbo, J. P. U., Richard, J., and Marchesini, D., E-mail: sgeier@astro.ku.dk. VLT/X-SHOOTER NEAR-INFRARED SPECTROSCOPY AND HST IMAGING OF GRAVITATIONALLY LENSED z ∼ 2 COMPACT QUIESCENT GALAXIES. United States: N. p., 2013. Web. doi:10.1088/0004-637X/777/2/87.
Geier, S., Man, A. W. S., Krühler, T., Toft, S., Fynbo, J. P. U., Richard, J., & Marchesini, D., E-mail: sgeier@astro.ku.dk. VLT/X-SHOOTER NEAR-INFRARED SPECTROSCOPY AND HST IMAGING OF GRAVITATIONALLY LENSED z ∼ 2 COMPACT QUIESCENT GALAXIES. United States. doi:10.1088/0004-637X/777/2/87.
Geier, S., Man, A. W. S., Krühler, T., Toft, S., Fynbo, J. P. U., Richard, J., and Marchesini, D., E-mail: sgeier@astro.ku.dk. Sun . "VLT/X-SHOOTER NEAR-INFRARED SPECTROSCOPY AND HST IMAGING OF GRAVITATIONALLY LENSED z ∼ 2 COMPACT QUIESCENT GALAXIES". United States. doi:10.1088/0004-637X/777/2/87.
@article{osti_22270654,
title = {VLT/X-SHOOTER NEAR-INFRARED SPECTROSCOPY AND HST IMAGING OF GRAVITATIONALLY LENSED z ∼ 2 COMPACT QUIESCENT GALAXIES},
author = {Geier, S. and Man, A. W. S. and Krühler, T. and Toft, S. and Fynbo, J. P. U. and Richard, J. and Marchesini, D., E-mail: sgeier@astro.ku.dk},
abstractNote = {Quiescent massive galaxies at z ∼ 2 are thought to be the progenitors of present-day massive ellipticals. Observations revealed them to be extraordinarily compact. Until now, the determination of stellar ages, star formation rates, and dust properties via spectroscopic measurements has been feasible only for the most luminous and massive specimens (∼3 × M*). Here we present a spectroscopic study of two near-infrared-selected galaxies that are close to the characteristic stellar mass M* (∼0.9 × M* and ∼1.3 × M*) and whose observed brightness has been boosted by the gravitational lensing effect. We measure the redshifts of the two galaxies to be z = 1.71 ± 0.02 and z = 2.15 ± 0.01. By fitting stellar population synthesis models to their spectrophotometric spectral energy distributions we determine their ages to be 2.4{sup +0.8}{sub -0.6} Gyr and 1.7 ± 0.3 Gyr, respectively, which implies that the two galaxies have higher mass-to-light ratios than most quiescent z ∼ 2 galaxies in other studies. We find no direct evidence for active star formation or active galactic nucleus activity in either of the two galaxies, based on the non-detection of emission lines. Based on the derived redshifts and stellar ages we estimate the formation redshifts to be z=4.3{sup +3.4}{sub -1.2} and z=4.3{sup +1.0}{sub -0.6}, respectively. We use the increased spatial resolution due to the gravitational lensing to derive constraints on the morphology. Fitting Sérsic profiles to the de-lensed images of the two galaxies confirms their compactness, with one of them being spheroid-like and the other providing the first confirmation of a passive lenticular galaxy at a spectroscopically derived redshift of z ∼ 2.},
doi = {10.1088/0004-637X/777/2/87},
journal = {Astrophysical Journal},
number = 2,
volume = 777,
place = {United States},
year = {Sun Nov 10 00:00:00 EST 2013},
month = {Sun Nov 10 00:00:00 EST 2013}
}
  • We analyze the star-forming and structural properties of 45 massive (log(M/M{sub ☉}) >10) compact star-forming galaxies (SFGs) at 2 < z < 3 to explore whether they are progenitors of compact quiescent galaxies at z ∼ 2. The optical/NIR and far-IR Spitzer/Herschel colors indicate that most compact SFGs are heavily obscured. Nearly half (47%) host an X-ray-bright active galactic nucleus (AGN). In contrast, only about 10% of other massive galaxies at that time host AGNs. Compact SFGs have centrally concentrated light profiles and spheroidal morphologies similar to quiescent galaxies and are thus strikingly different from other SFGs, which typically aremore » disk-like and sometimes clumpy or irregular. Most compact SFGs lie either within the star formation rate (SFR)-mass main sequence (65%) or below it (30%), on the expected evolutionary path toward quiescent galaxies. These results show conclusively that galaxies become more compact before they lose their gas and dust, quenching star formation. Using extensive HST photometry from CANDELS and grism spectroscopy from the 3D-HST survey, we model their stellar populations with either exponentially declining (τ) star formation histories (SFHs) or physically motivated SFHs drawn from semianalytic models (SAMs). SAMs predict longer formation timescales and older ages ∼2 Gyr, which are nearly twice as old as the estimates of the τ models. Both models yield good spectral energy distribution fits, indicating that the systematic uncertainty in the age due to degeneracies in the SFH is of that order of magnitude. However, SAM SFHs better match the observed slope and zero point of the SFR-mass main sequence. Contrary to expectations, some low-mass compact SFGs (log(M/M{sub ☉}) =10-10.6) have younger ages but lower specific SFRs than that of more massive galaxies, suggesting that the low-mass galaxies reach the red sequence faster. If the progenitors of compact SFGs are extended SFGs, state-of-the-art SAMs show that mergers and disk instabilities (DIs) are both able to shrink galaxies, but DIs are more frequent (60% versus 40%) and form more concentrated galaxies. We confirm this result via high-resolution hydrodynamic simulations.« less
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