Some of the most 'active' galaxies in the Universe are obscured by large quantities of dust and emit a substantial fraction of their bolometric luminosity in the infrared. Observations of these ...infrared luminous galaxies with the Infrared Space Observatory (ISO) have provided a relatively unabsorbed view to the sources fuelling this active emission. The improved sensitivity, spatial resolution and spectroscopic capability of ISO over its predecessor Infrared Astronomical Satellite (IRAS) of enabled significant advances in the understanding of the infrared properties of active galaxies. ISO surveyed a wide range of active galaxies which, in the context of this review, includes those powered by intense bursts of star formation as well as those containing a dominant active galactic nucleus (AGN). Mid-infrared imaging resolved for the first time the dust enshrouded nuclei in many nearby galaxies, while a new era in infrared spectroscopy was opened by probing a wealth of atomic, ionic and molecular lines as well as broad band features in the mid- and far-infrared. This was particularly useful, since it resulted in the understanding of the power production, excitation and fuelling mechanisms in the nuclei of active galaxies including the intriguing but so far elusive ultraluminous infrared galaxies. Detailed studies of various classes of AGN and quasars greatly improved our understanding of the unification scenario. Far-infrared imaging and photometry revealed the presence of a new very cold dust component in galaxies and furthered our knowledge of the far-infrared properties of faint starbursts, ULIGs and quasars. We summarise almost nine years of key results based on ISO data spanning the full range of luminosity and type of active galaxies.
We report new detections and limits from a NOEMA and ALMA CO(1-0) search for molecular outflows in 13 local galaxies with high far-infrared surface brightness, and combine these with local universe ...CO outflow results from the literature. The CO line ratios and spatial outflow structure of our targets provide some constraints on the conversion steps from observables to physical quantities such as molecular mass outflow rates. Where available, ratios between outflow emission in higher J CO transitions and in CO(1-0) are typically consistent with excitation
R
i
1
≲ 1. However, for IRAS 13120−5453,
R
31
= 2.10 ± 0.29 indicates optically thin CO in the outflow. Like much of the outflow literature, we use
α
CO(1 − 0)
= 0.8, and we present arguments for using
C
= 1 in deriving molecular mass outflow rates
Ṁ
out
=
C
M
out
v
out
/
R
out
. We compare the two main methods for molecular outflow detection: CO millimeter interferometry and
Herschel
OH-based spectroscopic outflow searches. For 26 sources studied with both methods, we find an 80% agreement in detecting
v
out
≳ 150 km s
−1
outflows, and non-matches can be plausibly ascribed to outflow geometry and signal-to-noise ratio. For a published sample of 12 bright ultraluminous infrared galaxies with detailed OH-based outflow modeling, CO outflows are detected in all but one. Outflow masses, velocities, and sizes for these 11 sources agree well between the two methods, and modest remaining differences may relate to the different but overlapping regions sampled by CO emission and OH absorption. Outflow properties correlate better with active galactic nucleus (AGN) luminosity and with bolometric luminosity than with far-infrared surface brightness. The most massive outflows are found for systems with current AGN activity, but significant outflows in nonAGN systems must relate to star formation or to AGN activity in the recent past. We report scaling relations for the increase of outflow mass, rate, momentum rate, and kinetic power with bolometric luminosity. Short flow times of ∼10
6
yr and some sources with resolved multiple outflow episodes support a role of intermittent driving, likely by AGNs.
We combine molecular gas masses inferred from CO emission in 500 star-forming galaxies (SFGs) between z = 0 and 3, from the IRAM-COLDGASS, PHIBSS1/2, and other surveys, with gas masses derived from ...Herschel far-IR dust measurements in 512 galaxy stacks over the same stellar mass/redshift range. We constrain the scaling relations of molecular gas depletion timescale (t sub(depl)) and gas to stellar mass ratio (M sub(mol gas)/Mlow *) of SFGs near the star formation "main-sequence" with redshift, specific star-formation rate (sSFR), and stellar mass (Mlow *). The CO- and dust-based scaling relations agree remarkably well. This suggests that the CO arrow right H sub(2) mass conversion factor varies little within + or -0.6 dex of the main sequence (sSFR(ms, z, Mlow *)), and less than 0.3 dex throughout this redshift range. This study builds on and strengthens the results of earlier work. We find that t sub(depl) scales as (1 + z) super(-0.3) x (sSFR/sSFR(ms, z, Mlow *)) super(-0.5), with little dependence on Mlow *. The resulting steep redshift dependence of M sub(mol gas)/Mlow * approximate (1 + z) super(3) mirrors that of the sSFR and probably reflects the gas supply rate. The decreasing gas fractions at high are driven by the flattening of the SFR-Mlow * relation. Throughout the probed redshift range a combination of an increasing gas fraction and a decreasing depletion timescale causes a larger sSFR at constant Mlow *. As a result, galaxy integrated samples of the M sub(mol gas)-SFR rate relation exhibit a super-linear slope, which increases with the range of sSFR. With these new relations it is now possible to determine M sub(mol gas) with an accuracy of + or -0.1 dex in relative terms, and + or -0.2 dex including systematic uncertainties.
ABSTRACT E+A galaxies are believed to be a short phase connecting major merger ultraluminous infrared galaxies (ULIRGs) with red and dead elliptical galaxies. Their optical spectrum suggests a ...massive starburst that was quenched abruptly, and their bulge-dominated morphologies with tidal tails suggest that they are merger remnants. Active galactic nucleus (AGN)-driven winds are believed to be one of the processes responsible for the sudden quenching of star formation and for the expulsion and/or destruction of the remaining molecular gas. Little is known about AGN-driven winds in this short-lived phase. In this paper, we present the first and unique sample of post-starburst galaxy candidates with AGNs that show indications of ionized outflows in their optical emission lines. Using Infrared Astronomical Satellite–far infrared (IRAS–FIR) observations, we study the star formation in these systems and find that many systems selected to have post-starburst signatures in their optical spectrum are in fact obscured starbursts. Using SDSS spectroscopy, we study the stationary and outflowing ionized gas. We also detect neutral gas outflows in 40 per cent of the sources with mass outflow rates 10–100 times more massive than in the ionized phase. The mean mass outflow rate and kinetic power of the ionized outflows in our sample ($\dot{M}\sim 1\, \mathrm{M_{\odot }\, yr^{-1}}$, $\dot{E}\sim 10^{41}\, \mathrm{erg\, s}^{-1}$) are larger than those derived for active galaxies of similar AGN luminosity and stellar mass. For the neutral outflow ($\dot{M}\sim 10\, \mathrm{M_{\odot }\, yr^{-1}}$, $\dot{E}\sim 10^{42}\, \mathrm{erg\, s}^{-1}$), their mean is smaller than that observed in (U)LIRGs with and without AGN.
We combine IRAM Plateau de Bure Interferometer and Herschel PACS and SPIRE measurements to study the dust and gas contents of high-redshift star-forming galaxies. We present new observations for a ...sample of 17 lensed galaxies at z = 1.4-3.1, which allow us to directly probe the cold interstellar medium of normal star-forming galaxies with stellar masses of ~10 super(10) M sub(middot in circle), a regime otherwise not (yet) accessible by individual detections in Herschel and molecular gas studies. The lensed galaxies are combined with reference samples of submillimeter and normal z ~ 1-2 star-forming galaxies with similar far-infrared photometry to study the gas and dust properties of galaxies in the SFR-M sub(*)-redshift parameter space. The depletion timescale and gas fractions of the z > 2 normal star-forming galaxies can be explained under the "equilibrium model" for galaxy evolution, in which the gas reservoir of galaxies is the primary driver of the redshift evolution of specific star formation rates.
We present measurements of the N ii/Hα ratio as a probe of gas-phase oxygen abundance for a sample of 419 star-forming galaxies at z = 0.6–2.7 from the KMOS{sup 3D} near-IR multi-integral field unit ...(IFU) survey. The mass–metallicity relation (MZR) is determined consistently with the same sample selection, metallicity tracer, and methodology over the wide redshift range probed by the survey. We find good agreement with long-slit surveys in the literature, except for the low-mass slope of the relation at z∼2.3, where this sample is less biased than previous samples based on optical spectroscopic redshifts. In this regime we measure a steeper slope than some literature results. Excluding the contribution from active galactic nuclei from the MZR reduces sensitivity at the high-mass end, but produces otherwise consistent results. There is no significant dependence of the N ii/Hα ratio on star formation rate at fixed redshift and stellar mass. The IFU data allow spatially resolved measurements of N ii/Hα, from which we can infer abundance gradients for 180 galaxies, thus tripling the current sample in the literature. The observed gradients are on average flat, with only 15 gradients statistically offset from zero at >3σ. We have modeled the effect of beam smearing, assuming a smooth intrinsic radial gradient and known seeing, inclination, and effective radius for each galaxy. Our seeing-limited observations can recover up to 70% of the intrinsic gradient for the largest, face-on disks, but only 30% for the smaller, more inclined galaxies. We do not find significant trends between observed or corrected gradients and any stellar population, dynamical, or structural galaxy parameters, mostly in agreement with existing studies with much smaller sample sizes. In cosmological simulations, strong feedback is generally required to produce flat gradients at high redshift.
ABSTRACT
Post-starburst galaxies are believed to be in a rapid transition between major merger starbursts and quiescent ellipticals. Their optical spectrum is dominated by A-type stars, suggesting a ...starburst that was quenched recently. While optical observations suggest little ongoing star formation, some have been shown to host significant molecular gas reservoirs. This led to the suggestion that gas depletion is not required to end the starburst, and that star formation is suppressed by other processes. We present NOEMA CO(1−0) observations of 15 post-starburst galaxies with emission lines consistent with active galactic nucleus (AGN) photoionization. We collect post-starburst candidates with molecular gas measurements from the literature, with some classified as classical E + A, while others with line ratios consistent with AGN and/or shock ionization. Using far-infrared observations, we show that systems that were reported to host exceptionally large molecular gas reservoirs host in fact obscured star formation, with some systems showing star formation rates comparable to ULIRGs. Among E + A galaxies with molecular gas measurements, 7 out of 26 (26 per cent) host obscured starbursts. Using far-infrared observations, post-starburst candidates show similar SFR–$M_{\mathrm{H_2}}$ and Kennicutt–Schmidt relations to those observed in star-forming and starburst galaxies. In particular, there is no need to hypothesize star formation quenching by processes other than the consumption of molecular gas by star formation. The combination of optical, far-infrared, and CO observations indicates that some regions within these galaxies have been recently quenched, while others are still forming stars in highly obscured regions. All this calls into question the traditional interpretation of such galaxies.
Exploiting the deep high-resolution imaging of all five CANDELS fields, and accurate redshift information provided by 3D-HST, we investigate the relation between structure and stellar populations for ...a mass-selected sample of 6764 galaxies above 10 super(10) M sub(middot in circle), spanning the redshift range 0.5 < z < 2.5. For the first time, we fit two-dimensional models comprising a single Sersic fit and two-component (i.e., bulge + disk) decompositions not only to the H-band light distributions, but also to the stellar mass maps reconstructed from resolved stellar population modeling. We confirm that the increased bulge prominence among quiescent galaxies, as reported previously based on rest-optical observations, remains in place when considering the distributions of stellar mass. Moreover, we observe an increase of the typical Sersic index and bulge-to-total ratio (with median B/T reaching 40%-50%) among star-forming galaxies above 10 super(11) M sub(middot in circle). Given that quenching for these most massive systems is likely to be imminent, our findings suggest that significant bulge growth precedes a departure from the star-forming main sequence. We demonstrate that the bulge mass (and ideally knowledge of the bulge and total mass) is a more reliable predictor of the star-forming versus quiescent state of a galaxy than the total stellar mass. The same trends are predicted by the state-of-the-art, semi-analytic model by Somerville et al. In this model, bulges and black holes grow hand in hand through merging and/or disk instabilities, and feedback from active galactic nuclei shuts off star formation. Further observations will be required to pin down star formation quenching mechanisms, but our results imply that they must be internal to the galaxies and closely associated with bulge growth.
ABSTRACT We present 0 2-resolution Atacama Large Millimeter/submillimeter Array observations at 870 m for 25 H -seleced star-forming galaxies around the main sequence at z = 2.2-2.5. We detect ...significant 870 m continuum emission in 16 (64%) of these galaxies. The high-resolution maps reveal that the dust emission is mostly radiated from a single region close to the galaxy center. Exploiting the visibility data taken over a wide uv distance range, we measure the half-light radii of the rest-frame far-infrared emission for the best sample of 12 massive galaxies with log(M*/M ) > 11. We find nine galaxies to be associated with extremely compact dust emission with R1/2,870 m < 1.5 kpc, which is more than a factor of 2 smaller than their rest-optical sizes, , and is comparable with optical sizes of massive quiescent galaxies at similar redshifts. As they have an exponential disk with Sérsic index of in the rest-optical, they are likely to be in the transition phase from extended disks to compact spheroids. Given their high star formation rate surface densities within the central 1 kpc of M yr−1 kpc−2, the intense circumnuclear starbursts can rapidly build up a central bulge with M*,1 kpc > 1010 M kpc−2 in several hundred megayears, i.e., by z ∼ 2. Moreover, ionized gas kinematics reveal that they are rotation supported with an angular momentum as large as that of typical star-forming galaxies at z = 1-3. Our results suggest that bulges are commonly formed in extended rotating disks by internal processes, not involving major mergers.
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