Far-infrared images and photometry are presented for 201 Luminous and Ultraluminous Infrared Galaxies LIRGs: log (L sub(IR)/L sub(middot in circle)) = 11.00-11.99, ULIRGs: log (L sub(IR)/L sub(middot ...in circle)) = 12.00-12.99, in the Great Observatories All-Sky LIRG Survey (GOALS), based on observations with the Herschel Space Observatory Photodetector Array Camera and Spectrometer (PACS) and the Spectral and Photometric Imaging Receiver (SPIRE) instruments. The image atlas displays each GOALS target in the three PACS bands (70, 100, and 160 mu m) and the three SPIRE bands (250, 350, and 500 mu m), optimized to reveal structures at both high and low surface brightness levels, with images scaled to simplify comparison of structures in the same physical areas of ~100 x 100 kpc super(2). Flux densities of companion galaxies in merging systems are provided where possible, depending on their angular separation and the spatial resolution in each passband, along with integrated system fluxes (sum of components). This data set constitutes the imaging and photometric component of the GOALS Herschel OT1 observing program, and is complementary to atlases presented for the Hubble Space Telescope, Spitzer Space Telescope, and Chandra X-ray Observatory. Collectively, these data will enable a wide range of detailed studies of active galactic nucleus and starburst activity within the most luminous infrared galaxies in the local universe.
Abstract
Mergers of galaxies are thought to cause significant gas inflows to the inner parsecs, which can activate rapid accretion on to supermassive black holes (SMBHs), giving rise to active ...galactic nuclei (AGN). During a significant fraction of this process, SMBHs are predicted to be enshrouded by gas and dust. Studying 52 galactic nuclei in infrared-selected local luminous and ultraluminous infrared galaxies in different merger stages in the hard X-ray band, where radiation is less affected by absorption, we find that the amount of material around SMBHs increases during the last phases of the merger. We find that the fraction of Compton-thick (CT, N H ≥ 1024 cm− 2) AGN in late-merger galaxies is higher ($f_{\rm \,CT}=65^{+12}_{-13}{\rm per\, cent}$) than in local hard X-ray selected AGN (f CT = 27 ± 4 per cent), and that obscuration reaches its maximum when the nuclei of the two merging galaxies are at a projected distance of D12 ≃ 0.4–10.8 kpc ($f_{\rm \,CT}=77_{-17}^{+13}{\rm per\, cent}$). We also find that all AGN of our sample in late-merger galaxies have N H > 1023 cm− 2, which implies that the obscuring material covers $95^{+4}_{-8}{\rm per\, cent}$ of the X-ray source. These observations show that the material is most effectively funnelled from the galactic scale to the inner tens of parsecs during the late stages of galaxy mergers, and that the close environment of SMBHs in advanced mergers is richer in gas and dust with respect to that of SMBHs in isolated galaxies, and cannot be explained by the classical AGN unification model in which the torus is responsible for the obscuration.
Galactic superwinds occur in almost all infrared-luminous galaxies with star formation rates (SFRs) above 10 M sub( )yr super(-1), as shown by studies of the Na I D interstellar absorption line. We ...demonstrate that this result also applies to ultraluminous infrared galaxies (ULIRGs) that host an active galactic nucleus (AGN) embedded in a strong starburst (SFR 100 M sub( )yr super(-1)) by studying a sample of 26 Seyfert ULIRGs in Na I D. The infrared luminosity of these galaxies is powered jointly by the AGN and starburst. We find that there are hints of the influence of the AGN on outflows in Seyfert 2/starburst composites, but the evidence is not yet statistically conclusive. The evidence we find is lower wind detection rates (i.e., wind opening angles) in Seyfert 2 ULIRGs than in galaxies of comparable L sub(IR), higher velocities than in galaxies of comparable SFR, and correlations between the neutral gas and the ionized gas in the extended narrow-line region. Although the AGN probably contributes to the outflows in Seyfert 2 ULIRGs, its momentum and energy injection is equal to or less than that of the starburst. Similarly, the outflow mechanical luminosity (energy outflow rate) per unit radiative luminosity is the same for starburst and Seyfert 2 ULIRGs. In the nuclei of Seyfert 1 ULIRGs, we observe small-scale outflows that are powered solely by the AGN. However, in Mrk 231, we observe both a high-velocity, small-scale and low-velocity, extended outflow. The latter may be powered by a starburst or radio jet. These large-scale, lower velocity outflows certainly exist in other Seyfert 1 ULIRGs, but they are washed out by the light of the nucleus.
ABSTRACT
We report the discovery of a Milky Way satellite in the constellation of Antlia. The Antlia 2 dwarf galaxy is located behind the Galactic disc at a latitude of b ∼ 11° and spans 1.26°, which ...corresponds to ∼2.9 kpc at its distance of 130 kpc. While similar in spatial extent to the Large Magellanic Cloud, Antlia 2 is orders of magnitude fainter at MV = −9 mag, making it by far the lowest surface brightness system known (at ∼31.9 mag arcsec−2), ∼100 times more diffuse than the so-called ultra diffuse galaxies. The satellite was identified using a combination of astrometry, photometry, and variability data from Gaia Data Release 2, and its nature confirmed with deep archival DECam imaging, which revealed a conspicuous BHB signal. We have also obtained follow-up spectroscopy using AAOmega on the AAT, identifying 159 member stars, and we used them to measure the dwarf’s systemic velocity, 290.9 ± 0.5 km s−1, its velocity dispersion, 5.7 ± 1.1 km s−1, and mean metallicity, Fe/H = −1.4. From these properties we conclude that Antlia 2 inhabits one of the least dense dark matter (DM) haloes probed to date. Dynamical modelling and tidal-disruption simulations suggest that a combination of a cored DM profile and strong tidal stripping may explain the observed properties of this satellite. The origin of this core may be consistent with aggressive feedback, or may even require alternatives to cold dark matter (such as ultra-light bosons).
We have performed an absorption-line survey of outflowing gas in 78 starburst-dominated, infrared-luminous galaxies. This is the largest study of superwinds at z 3. Superwinds are found in almost all ...infrared-luminous galaxies, and changes in detection rate with SRF--winds are found twice as often in ultraluminous infrared galaxies (ULIRGs) as in less-luminous galaxies-reflect different wind geometries. The maximum velocities we measure are 600 km s super(-1), though most of the outflowing gas has lower velocities (100-200 km s super(-1)). (One galaxy has velocities exceeding 1000 km s super(-1).) Velocities in LINERs are higher than in H II galaxies, and outflowing ionized gas often has higher velocities than the neutral gas. Wind properties (velocity, mass, momentum, and energy) scale with galaxy properties (SFR, luminosity, and galaxy mass), consistent with ram-pressure driving of the wind. Wind properties increase strongly with increasing galactic mass, contrary to expectation. These correlations flatten at high SFR ( 10-100 M sub( )yr super(-1)), luminosities, and masses. This saturation is due to a lack of gas remaining in the wind's path, a common neutral gas terminal velocity, and/or a decrease in the efficiency of thermalization of the supernovae energy. It means that mass entrainment efficiency, rather than remaining constant, declines in galaxies with SFR > 10 M sub( )yr super(-1) and M sub(K) < -24. Half of our sample consists of ULIRGs, which host as much as half of the star formation in the universe at z 1. The powerful, ubiquitous winds we observe in these galaxies imply that superwinds in massive galaxies at redshifts above unity play an important role in the evolution of galaxies and the intergalactic medium.
We investigate the fraction of starbursts, starburst-active galactic nucleus (AGN) composites, Seyferts, and low-ionization narrow emission-line region galaxies (LINERs) as a function of infrared ...luminosity (L{sub IR}) and merger progress for approx500 infrared (IR)-selected galaxies. Using the new optical classifications afforded by the extremely large data set of the Sloan Digital Sky Survey, we find that the fraction of LINERs in IR-selected samples is rare (<5%) compared with other spectral types. The lack of strong IR emission in LINERs is consistent with recent optical studies suggesting that LINERs contain AGN with lower accretion rates than in Seyfert galaxies. Most previously classified IR-luminous LINERs are classified as starburst-AGN composite galaxies in the new scheme. Starburst-AGN composites appear to 'bridge' the spectral evolution from starburst to AGN in ULIRGs. The relative strength of the AGN versus starburst activity shows a significant increase at high IR luminosity. In ULIRGs (L{sub IR} > 10{sup 12} L{sub sun}), starburst-AGN composite galaxies dominate at early-intermediate stages of the merger, and AGN galaxies dominate during the final merger stages. Our results are consistent with models for IR-luminous galaxies where mergers of gas-rich spirals fuel both starburst and AGN, and where the AGN becomes increasingly dominant during the final merger stages of the most luminous IR objects.
Spitzer/IRAC selection is a powerful tool for identifying luminous active galactic nuclei (AGNs). For deep IRAC data, however, the AGN selection wedges currently in use are heavily contaminated by ...star-forming galaxies, especially at high redshift. Using the large samples of luminous AGNs and high-redshift star-forming galaxies in COSMOS, we redefine the AGN selection criteria for use in deep IRAC surveys. The new IRAC criteria are designed to be both highly complete and reliable, and incorporate the best aspects of the current AGN selection wedges and of infrared power-law selection while excluding high-redshift star-forming galaxies selected via the BzK, distant red galaxy, Lyman-break galaxy, and submillimeter galaxy criteria. At QSO luminosities of log L sub(2-10 keV)(erg s super(-1)) > or =, slanted 44, the new IRAC criteria recover 75% of the hard X-ray and IRAC-detected XMM-COSMOS sample, yet only 38% of the IRAC AGN candidates have X-ray counterparts, a fraction that rises to 52% in regions with Chandra exposures of 50-160 ks. X-ray stacking of the individually X-ray non-detected AGN candidates leads to a hard X-ray signal indicative of heavily obscured to mildly Compton-thick obscuration (log N sub(H) (cm super(-2)) = 23.5 + or - 0.4). While IRAC selection recovers a substantial fraction of luminous unobscured and obscured AGNs, it is incomplete to low-luminosity and host-dominated AGNs.
The so-called star-forming main sequence of galaxies is the apparent tight relationship between the star formation rate and stellar mass of a galaxy. Many studies exclude galaxies which are not ...strictly ‘star forming’ from the main sequence, because they do not lie on the same tight relation. Using local galaxies in the Sloan Digital Sky Survey, we have classified galaxies according to their emission line ratios, and studied their location on the star formation rate–stellar mass plane. We find that galaxies form a sequence from the ‘blue cloud’ galaxies which are actively forming stars, through a combination of composite, Seyfert, and low-ionization nuclear emission-line region galaxies, ending as ‘red-and-dead’ galaxies. The sequence supports an evolutionary pathway for galaxies in which star formation quenching by active galactic nuclei plays a key role.
We used the COSMOS2020 catalog to measure the stellar-to-halo mass relation (SHMR) divided by central and satellite galaxies from
z
= 0.2 to
z
= 5.5. Starting from accurate photometric redshifts, ...we measured the near-infrared selected two-point angular correlation and stellar mass functions in ten redshift bins. We used a phenomenological model that parametrizes the stellar-to-halo mass relation for central galaxies and the number of galaxies inside each halo to describe our observations. This model qualitatively reproduces our measurements and their dependence on the stellar mass threshold. Surprisingly, the mean halo occupation distribution only shows a mild evolution with redshift suggesting that galaxies occupy halos similarly throughout cosmic time. At each redshift, we measured the ratio of stellar mass to halo mass,
M
*
/
M
h
, which shows the characteristic strong dependence of halo mass with a peak at
M
h
peak
∼ 2 × 10
12
M
⊙
. For the first time, using a joint modeling of clustering and abundances, we measured the evolution of
M
h
peak
from
z
= 0.2 to
z
= 5.5.
M
h
peak
increases gradually with redshift from log
M
h
peak
/
M
⊙
∼ 12.1 at
z
∼ 0.3 to log
M
h
peak
/
M
⊙
∼ 12.3 at
z
∼ 2, and up to log
M
h
peak
/
M
⊙
∼ 12.9 at
z
∼ 5. Similarly, the stellar mass peak
M
∗
peak
increases with redshift from log
M
∗
peak
/
M
⊙
∼ 10.5 at
z
∼ 0.3 to log
M
∗
peak
/
M
⊙
∼ 10.9 at
z
∼ 3. The SHMR ratio at the peak halo mass remains almost constant with redshift. These results are in accordance with the scenario in which the peak of star-formation efficiency moves toward more massive halos at higher redshifts. We also measured the fraction of satellites as a function of stellar mass and redshift. For all stellar mass thresholds, the satellite fraction decreases at higher redshifts. At a given redshift, there is a higher fraction of low-mass satellites and this fraction reaches a plateau at ∼25% at
z
∼ 1. The satellite contribution to the total stellar mass budget in halos becomes more important than that of the central at halo masses of about
M
h
> 10
13
M
⊙
and always stays below the peak, indicating that quenching mechanisms are present in massive halos that keep the star-formation efficiency low. Finally, we compared our results with three hydrodynamical simulations: H
ORIZON
-AGN, TNG100 of the I
LLUSTRIS
TNG project, and EAGLE. We find that the most significant discrepancy is at the high-mass end, where the simulations generally show that satellites have a higher contribution to the total stellar mass budget than the observations. This, together with the finding that the fraction of satellites is higher in the simulations, indicates that the feedback mechanisms acting in both group- and cluster-scale halos appear to be less efficient in quenching the mass assembly of satellites – and that quenching occurs much later in the simulations.
We present an empirical method of assessing the star formation rate (SFR) of star-forming galaxies based on their locations in the rest-frame color–color diagram (NUV − r) vs. (r − K). By using the ...Spitzer 24 μm sample in the COSMOS field (~16 400 galaxies with 0.2 ≤ z ≤ 1.3) and a local GALEX-SDSS-SWIRE sample (~700 galaxies with z ≤ 0.2), we show that the mean infrared excess ⟨IRX⟩ = ⟨ LIR/LUV ⟩ can be described by a single vector, NRK , that combines the two colors. The calibration between ⟨IRX⟩ and NRK allows us to recover the IR luminosity, LIR, with an accuracy of σ ~ 0.21 for the COSMOS sample and 0.27 dex for the local one. The SFRs derived with this method agree with the ones based on the observed (UV+IR) luminosities and on the spectral energy distribution (SED) fitting for the vast majority (~85%) of the star-forming population. Thanks to a library of model galaxy SEDs with realistic prescriptions for the star formation history, we show that we need to include a two-component dust model (i.e., birth clouds and diffuse ISM) and a full distribution of galaxy inclinations in order to reproduce the behavior of the ⟨IRX⟩ stripes in the NUVrK diagram. In conclusion, the NRK method, based only on the rest-frame UV/optical colors available in most of the extragalactic fields, offers a simple alternative of assessing the SFR of star-forming galaxies in the absence of far-IR or spectral diagnostic observations.
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