M. Ashby

CANDELS+3D-HST: COMPACT SFGs AT z ∼ 2-3, THE PROGENITORS OF THE FIRST QUIESCENT GALAXIES

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 are 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 nearlymorexa0» 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.«xa0less

Revealing the Heavily Obscured Active Galactic Nucleus Population of High-redshift 3CRR Sources with Chandra X-Ray Observations

Chandra observations of a complete, flux-limited sample of 38 high-redshift (1 0) indicating obscuration (N_H ~10^(22)-10^(24) cm^(–2)). These properties and the correlation between obscuration and radio core fraction are consistent with orientation-dependent obscuration as in unification models. About half the NLRGs have soft X-ray hardness ratios and/or a high [O III] emission line to X-ray luminosity ratio suggesting obscuration by Compton thick (CT) material so that scattered nuclear or extended X-ray emission dominates (as in NGC 1068). The ratios of unobscured to Compton-thin (10^(22) cm^(–2) 1.5 × 10^(24) cm^(–2)) is 2.5:1.4:1 in this high-luminosity, radio-selected sample. The obscured fraction is 0.5, higher than is typically reported for active galactic nuclei at comparable luminosities from multi-wavelength surveys (0.1-0.3). Assuming random nuclear orientation, the unobscured half-opening angle of the disk/wind/torus structure is ~60° and the obscuring material covers 30°, ~12° of which is CT. The multi-wavelength properties reveal that many NLRGs have intrinsic absorption 10-1000 × higher than indicated by their X-ray hardness ratios, and their true L_X values are ~10-100× larger than the hardness-ratio absorption corrections would indicate.

Star-forming blue etgs in two newly discovered galaxy overdensities in the HUDF at z = 1.84 and 1.9: unveiling the progenitors of passive ETGs in cluster cores

We present the discovery of two galaxy overdensities in the Hubble Space Telescope UDF: a proto-cluster, HUDFJ0332.4-2746.6 at z=1.84 ± 0.01, and a group, HUDFJ0332.5-2747.3 at z=1.90 ± 0.01. Assuming viralization, the velocity dispersion of HUDFJ0332.4-2746.6 implies a mass of M_(200) = (2.2 ± 1.8) x 10^(14) M_☉, consistent with the lack of extended X-ray emission. Neither overdensity shows evidence of a red sequence. About

HIGH-LYING OH ABSORPTION, [C II] DEFICITS, AND EXTREME L FIR/M H2 RATIOS IN GALAXIES

50%

Chandra X-ray Observations of the Redshift 1.53 Radio-Loud Quasar 3C 270.1

of their members show interactions and/or disturbed morphologies, which are signatures of merger remnants or disk instability. Most of their ETGs have blue colors and show recent star formation. These observations reveal for the first time large fractions of spectroscopically confirmed star-forming blue ETGs in proto-clusters at ≈ z. These star-forming ETGs are most likely among the progenitors of the quiescent population in clusters at more recent epochs. Their mass–size relation is consistent with that of passive ETGs in clusters at z ~ 0.7-1.5. If these galaxies are the progenitors of cluster ETGs at these lower redshifts, their size would evolve according to a similar mass-size relation. It is noteworthy that quiescent ETGs in clusters at z = 1.8-2 also do not show any significant size evolution over this redshift range, contrary to field ETGs. The ETG fraction is ≾50%, compared to the typical quiescent ETG fraction of ≈80% in cluster cores at z < 1. The fraction, masses, and colors of the newly discovered ETGs imply that other cluster ETGs will be formed/accreted at a later time.

PdBI cold dust imaging of two extremely red H – [4.5] > 4 galaxies discovered with SEDS and CANDELS

Herschel/PACS observations of 29 local (ultra)luminous infrared galaxies, including both starburst and active galactic nucleus (AGN) dominated sources as diagnosed in the mid-infrared/optical, show that the equivalent width of the absorbing OH 65 μm Π_(3/2) J = 9/2-7/2 line (W_(eq)(OH65)) with lower level energy E_(low) ≈ 300 K, is anticorrelated with the [C II]158 μm line to far-infrared luminosity ratio, and correlated with the far-infrared luminosity per unit gas mass and with the 60-to-100 μm far-infrared color. While all sources are in the active L_(IR)/M_(H2) > 50L_☉/M_☉ mode as derived from previous CO line studies, the OH65 absorption shows a bimodal distribution with a discontinuity at L_(FIR)/M_(H2) ≈ 100 L_☉/M_☉. In the most buried sources, OH65 probes material partially responsible for the silicate 9.7 μm absorption. Combined with observations of the OH 71 μm Π_(1/2) J = 7/2-5/2 doublet (E_(low) ≈ 415 K), radiative transfer models characterized by the equivalent dust temperature, T_(dust), and the continuum optical depth at 100 μm, τ_(100), indicate that strong [C_(II)]158 μm deficits are associated with far-IR thick (τ_(100) ≳ 0.7, N_H ≳ 10^(24) cm^(–2)), warm (T_(dust) ≳ 60 K) structures where the OH 65 μm absorption is produced, most likely in circumnuclear disks/tori/cocoons. With their high L_(FIR)/M_(H2) ratios and columns, the presence of these structures is expected to give rise to strong [C_(II)] deficits. W_(eq)(OH65) probes the fraction of infrared luminosity arising from these compact/warm environments, which is ≳ 30%-50% in sources with high W_(eq)(OH65). Sources with high W_(eq)(OH65) have surface densities of both L_(IR) and M_(H2) higher than inferred from the half-light (CO or UV/optical) radius, tracing coherent structures that represent the most buried/active stage of (circum)nuclear starburst-AGN co-evolution.

AAS/High Energy Astrophysics Division

Chandra X-ray observations of the high redshift (z = 1.532) radio-loud quasar 3C 270.1 in 2008 February show the nucleus to have a power-law spectrum, Γ = 1.66 ± 0.08, typical of a radio-loud quasar, and a marginally detected Fe Kα emission line. The data also reveal extended X-ray emission, about half of which is associated with the radio emission from this source. The southern emission is co-spatial with the radio lobe and peaks at the position of the double radio hot spot. Modeling this hot spot, including Spitzer upper limits, rules out synchrotron emission from a single power-law population of electrons, favoring inverse Compton emission with a field of ~11 nT, roughly a third of the equipartition value. The northern emission is concentrated close to the location of a 40° bend where the radio jet is presumed to encounter an external medium. It can be explained by inverse Compton emission involving cosmic microwave background photons with a field of ~3 nT, a factor of 7-10 below the equipartition value. The remaining, more diffuse X-ray emission is harder (HR = –0.09 ± 0.22). With only 22.8 ± 5.6 counts, the spectral form cannot be constrained. Assuming thermal emission with a temperature of 4 keV yields an estimate for the luminosity of 1.8× 10^(44) erg s^(–1), consistent with the luminosity-temperature relation of lower-redshift clusters. However, deeper Chandra X-ray observations are required to delineate the spatial distribution and better constrain the spectrum of the diffuse emission to verify that we have detected X-ray emission from a high-redshift cluster.

High-lying OH Absorption, [C_(II)] Deficits, and Extreme L_(FIR)/M_(H2) Ratios in Galaxies

We report Plateau de Bure Interferometer (PdBI) 1.1 mm continuum imaging toward two extremely red H - [4.5] > 4 (AB) galaxies at z > 3, which we have previously discovered making use of Spitzer SEDS and Hubble Space Telescope CANDELS ultra-deep images of the Ultra Deep Survey field. One of our objects is detected on the PdBI map with a 4.3σ significance, corresponding to S_nu (1.1 , mm)=0.78 +/- 0.18 , mJy. By combining this detection with the Spitzer 8 and 24 μm photometry for this source, and SCUBA2 flux density upper limits, we infer that this galaxy is a composite active galactic nucleus/star-forming system. The infrared (IR)-derived star formation rate is SFR ≈ 200 ± 100 M ⊙ yr-1, which implies that this galaxy is a higher-redshift analogue of the ordinary ultra-luminous infrared galaxies more commonly found at z ~ 2-3. In the field of the other target, we find a tentative 3.1σ detection on the PdBI 1.1 mm map, but 3.7 arcsec away of our target position, so it likely corresponds to a different object. In spite of the lower significance, the PdBI detection is supported by a close SCUBA2 3.3σ detection. No counterpart is found on either the deep SEDS or CANDELS maps, so, if real, the PdBI source could be similar in nature to the submillimeter source GN10. We conclude that the analysis of ultra-deep near- and mid-IR images offers an efficient, alternative route to discover new sites of powerful star formation activity at high redshifts.