Stellar kinematics provide insights into the masses and formation histories of galaxies. At high redshifts, spatially resolving the stellar kinematics of quiescent galaxies is challenging due to ...their compact sizes. Using deep near-infrared spectroscopy, we have measured the resolved stellar kinematics of four quiescent galaxies at z = 1.95-2.64, introduced in Paper I, that are gravitationally lensed by galaxy clusters. Analyses of two of these have previously been reported individually by Newman et al. and Toft et al., and for the latter, we present new observations. All four galaxies show significant rotation and can be classified as "fast rotators." In the three systems for which the lensing constraints permit a reconstruction of the source, we find that all are likely to be highly flattened (intrinsic ellipticities of 0.75-0.85) disk-dominated galaxies with rapid rotation speeds of Vmax = 290-352 km s−1 and predominantly rotational support, as indicated by the ratio Compared to coeval star-forming galaxies of similar mass, the quiescent galaxies have smaller V/ . Given their high masses, , we argue that these galaxies are likely to evolve into "slow rotator" elliptical galaxies whose specific angular momentum is reduced by a factor of 5-10. This provides strong evidence for merger-driven evolution of massive galaxies after quenching. Consistent with indirect evidence from earlier morphological studies, our small but unique sample suggests that the kinematic transformations that produced round, dispersion-supported elliptical galaxies were not generally coincident with quenching. Such galaxies probably emerged later via mergers that increased their masses and sizes while also eroding their rotational support.
Abstract
We study the recent star formation histories (SFHs) of 575 intermediate-mass galaxies (IMGs, 10
9
≤
M
/
M
⊙
≤ 10
10
) in COSMOS at 0.3 <
z
< 0.4 by comparing their H
α
and UV luminosities. ...These two measurements trace star formation rates (SFRs) on different timescales and together reveal fluctuations in recent activity. We compute
L
H
α
from Magellan IMACS spectroscopy, while
L
UV
is derived from rest-frame 2800 Å photometry. Dust corrections are applied to each band independently. We compare the deviation of
L
H
α
and
L
UV
from their respective star-forming sequences (i.e.,
Δ
log
L
H
α
and
Δ
log
L
UV
), and after accounting for observational uncertainties we find a small intrinsic scatter between the two quantities (
σ
δ
≲ 0.03 dex). This crucial observational constraint precludes strong fluctuations in the recent SFHs of IMGs: simple linear SFH models indicate that a population of IMGs would be limited to only factors of ≲2 change in SFR over 200 Myr and ≲30% on shorter timescales of 20 Myr. No single characteristic SFH for IMGs, such as an exponentially rising/falling burst, can reproduce the individual and joint distribution of
Δ
log
L
H
α
and
Δ
log
L
UV
. Instead, an ensemble of SFHs is preferred. Finally, we find that IMG SFHs predicted by recent hydrodynamic simulations, in which feedback drives rapid and strong SFR fluctuations, are inconsistent with our observations.
We present nearly 500 days of observations of the tidal disruption event (TDE) ASASSN-18pg, spanning from 54 days before peak light to 441 days after peak light. Our data set includes X-ray, UV, and ...optical photometry, optical spectroscopy, radio observations, and the first published spectropolarimetric observations of a TDE. ASASSN-18pg was discovered on 2018 July 11 by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of d = 78.6 Mpc; with a peak UV magnitude of m 14, it is both one of the nearest and brightest TDEs discovered to-date. The photometric data allow us to track both the rise to peak and the long-term evolution of the TDE. ASASSN-18pg peaked at a luminosity of L 2.4 × 1044 erg s−1, and its late-time evolution is shallower than a flux ∝t−5/3 power-law model, similar to what has been seen in other TDEs. ASASSN-18pg exhibited Balmer lines and spectroscopic features consistent with Bowen fluorescence prior to peak, which remained detectable for roughly 225 days after peak. Analysis of the two-component H profile indicates that, if they are the result of reprocessing of emission from the accretion disk, the different spectroscopic lines may be coming from regions between ∼10 and ∼60 lt-days from the black hole. No X-ray emission is detected from the TDE, and there is no evidence of a jet or strong outflow detected in the radio. Our spectropolarimetric observations indicate that the projected emission region is likely not significantly aspherical, with the projected emission region having an axis ratio of 0.65.
We study the structural evolution of massive galaxies by linking progenitors and descendants at a constant cumulative number density of nsubc = 1.4 x 10sup -4 Mpcsup -3 to z ~ 3. Structural ...parameters were measured by fitting Sersic profiles to high-resolution CANDELS HST WFC3 Jsub 125 and Hsub 160 imaging in the UKIDSS-UDS at 1 < z < 3 and ACS Isub 814 imaging in COSMOS at 0.25 < z < 1. At a given redshift, we selected the HST band that most closely samples a common rest-frame wavelength so as to minimize systematics from color gradients in galaxies. Toward lower redshifts, these galaxies continued to assemble mass at larger radii and became the local ellipticals that dominate the high-mass end of the mass function at the present epoch.
Filaments of the cosmic web have long been associated with the threadlike structures seen in galaxy redshift surveys. However, despite their baryon content being dominated by hot gas, these filaments ...have been an elusive target for X-ray observations. Recently, detections of filaments in very deep (2.4 Ms) observations with Chandra were reported around Abell 133 (z = 0.0559). To verify these claims, we conducted a multiobject spectrographic campaign on the Baade 6.5 m telescope around Abell 133; this resulted in a catalog of ∼3000 new redshift measurements, of which 254 are of galaxies near the cluster. We investigate the kinematic state of Abell 133 and identify the physical locations of filamentary structure in the galaxy distribution. Contrary to previous studies, we see no evidence that Abell 133 is dynamically disturbed; we reject the hypothesis that there is a kinematically distinct subgroup (p = 0.28) and find no velocity offset between the central galaxy and the cluster ( ). The spatial distribution of galaxies traces the X-ray filaments, as confirmed by angular cross-correlation with a significance of ∼5 . A similar agreement is found in the angular density distribution, where two X-ray structures have corresponding galaxy enhancements. We also identify filaments in the large-scale structure of galaxies; these filaments approach the cluster from the direction the X-ray structures are seen. While more members between R200 and 2 × R200 are required to clarify which large-scale filaments connect to the X-ray gas, we argue that this is compelling evidence that the X-ray emission is indeed associated with cosmic filaments.
The 3D-HST and CANDELS programs have provided WFC3 and ACS spectroscopy and photometry over approximate900 arcmin super(2) in five fields: AEGIS, COSMOS, GOODS-North, GOODS-South, and the UKIDSS UDS ...field. All these fields have a wealth of publicly available imaging data sets in addition to the Hubble Space Telescope (HST) data, which makes it possible to construct the spectral energy distributions (SEDs) of objects over a wide wavelength range. In this paper we describe a photometric analysis of the CANDELS and 3D-HST HST imaging and the ancillary imaging data at wavelengths 0.3-8Mum. Objects were selected in the WFC3 near-IR bands, and their SEDs were determined by carefully taking the effects of the point-spread function in each observation into account. A total of 147 distinct imaging data sets were used in the analysis. The photometry is made available in the form of six catalogs: one for each field, as well as a master catalog containing all objects in the entire survey. We also provide derived data products: photometric redshifts, determined with the EAZY code, and stellar population parameters determined with the FAST code. We make all the imaging data that were used in the analysis available, including our reductions of the WFC3 imaging in all five fields. 3D-HST is a spectroscopic survey with the WFC3 and ACS grisms, and the photometric catalogs presented here constitute a necessary first step in the analysis of these grism data. All the data presented in this paper are available through the 3D-HST Web site (http://3dhst.research.yale.edu).
Measuring the chemical composition of galaxies is crucial to our understanding of galaxy formation and evolution models. However, such measurements are extremely challenging for quiescent galaxies at ...high redshifts, which have faint stellar continua and compact sizes, making it difficult to detect absorption lines and nearly impossible to spatially resolve them. Gravitational lensing offers the opportunity to study these galaxies with detailed spectroscopy that can be spatially resolved. In this work, we analyze deep spectra of MRG-M0138, a lensed quiescent galaxy at z = 1.98, which is the brightest of its kind, with an H-band magnitude of 17.1. Taking advantage of full spectral fitting, we measure Mg/Fe = 0.51 0.05, Fe/H = 0.26 0.04, and, for the first time, the stellar abundances of six other elements in this galaxy. We further constrained, also for the first time in a z ∼ 2 galaxy, radial gradients in stellar age, Fe/H, and Mg/Fe. We detect no gradient in age or Mg/Fe and a slightly negative gradient in Fe/H, which has a slope comparable to that seen in local early-type galaxies. Our measurements show that not only is MRG-M0138 very Mg-enhanced compared to the centers of local massive early-type galaxies, it is also very iron rich. These dissimilar abundances suggest that even the inner regions of massive galaxies have experienced significant mixing of stars in mergers, in contrast to a purely inside-out growth model. The abundance pattern observed in MRG-M0138 challenges simple galactic chemical evolution models that vary only the star formation timescale and shows the need for more elaborate models.
ABSTRACT Using the Hubble Space Telescope (HST)/WFC3 and Advanced Camera for Surveys multi-band imaging data taken in CANDELS and 3D-HST, we study the general properties and diversity of the ...progenitors of the Milky Way (MWs) and local massive galaxy (MGs) at , based on a constant cumulative number density analysis. After careful data reduction and stacking analysis, we conduct a radially resolved pixel spectral energy distribution fitting to obtain the radial distributions of the stellar mass and rest-frame colors. The stellar mass of MWs increases in a self-similar way, irrespective of the radial distance, while that of MGs grows in an inside-out way where they obtain of the total mass at the outer ( kpc) radius since . Although the radial mass profiles evolve in distinct ways, the formation and quenching of the central dense region (or bulge) ahead of the formation of the outer disk are found to be common for both systems. The sudden reddening of the bulge at and for MWs and MGs, respectively, suggests the formation of the bulge and would give a clue to the different gas accretion histories and quenching. A new approach to evaluate the morphological diversity is conducted by using the average surface density profile and its dispersion. The variety of the radial mass profiles for MGs peaks at higher redshift ( ) and then rapidly converges to a more uniform shape at , while that for MWs remains in the outer region over the redshift. Compared with the observed star-formation rates and color profiles, the evolution of variety is consistently explained by the star-formation activities.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted) Quiescent galaxies at z ~ 2 have been identified in large numbers based on rest-frame colors, but only a small number of these ...galaxies have been spectroscopically confirmed to show that their rest-frame optical spectra show either strong Balmer or metal absorption lines. Here, we median stack the rest-frame optical spectra for 171 photometrically quiescent galaxies at 1.4 < z < 2.2 from the 3D-HST grism survey. In addition to H beta (lambda4861 Angstrom), we unambiguously identify metal absorption lines in the stacked spectrum, including the G band (lambda4304 Angstrom), Mg I (lambda5175 Angstrom), and Na I (lambda5894 Angstrom). This finding demonstrates that galaxies with relatively old stellar populations already existed when the universe was ~3 Gyr old, and that rest-frame color selection techniques can efficiently select them. We find an average age of ... Gyr when fitting a simple stellar population to the entire stack. We confirm our previous result from medium-band photometry that the stellar age varies with the colors of quiescent galaxies: the reddest 80% of galaxies are dominated by metal lines and have a relatively old mean age of ... Gyr, whereas the bluest (and brightest) galaxies have strong Balmer lines and a spectroscopic age of ... Gyr. Although the spectrum is dominated by an evolved stellar population, we also find OIII and H beta emission. Interestingly, this emission is more centrally concentrated than the continuum with L sub(O III) = 1.7 + or - 0.3 x 10 super(40) erg s super(-1), indicating residual central star formation or nuclear activity.
We investigate star formation rates (SFRs) of quiescent galaxies at high redshift (0.3 < z < 2.5) using 3D-HST WFC3 grism spectroscopy and Spitzer mid-infrared data. We select quiescent galaxies on ...the basis of the widely used UVJ color-color criteria. Spectral energy distribution (SED) fitting (rest-frame optical and near-IR) indicates very low SFRs for quiescent galaxies (sSFR ~ 10 super(-12) yr super(-1)). However, SED fitting can miss star formation if it is hidden behind high dust obscuration and ionizing radiation is re-emitted in the mid-infrared. It is therefore fundamental to measure the dust-obscured SFRs with a mid-IR indicator. We stack the MIPS 24 mum images of quiescent objects in five redshift bins centered on z = 0.5, 0.9, 1.2, 1.7, 2.2 and perform aperture photometry. Including direct 24 mum detections, we find sSFR ~ 10 super(-11.9) x(1 + z) super(4) yr super(-1). These values are higher than those indicated by SED fitting, but at each redshift they are 20-40 times lower than those of typical star-forming galaxies. The true SFRs of quiescent galaxies might be even lower, as we show that the mid-IR fluxes can be due to processes unrelated to ongoing star formation, such as cirrus dust heated by old stellar populations and circumstellar dust. Our measurements show that star formation quenching is very efficient at every redshift. The measured SFR values are at z > 1.5 marginally consistent with the ones expected from gas recycling (assuming that mass loss from evolved stars refuels star formation) and well below that at lower redshifts.
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