We study the properties of massive, galactic-scale outflows of molecular gas and investigate their impact on galaxy evolution. We present new IRAM PdBI CO(1–0) observations of local ultra-luminous ...infrared galaxies (ULIRGs) and quasar-hosts: a clear signature of massive and energetic molecular outflows, extending on kpc scales, is found in the CO(1–0) kinematics of four out of seven sources, with measured outflow rates of several 100 M⊙ yr-1. We combine these new observations with data from the literature, and explore the nature and origin of massive molecular outflows within an extended sample of 19 local galaxies. We find that starburst-dominated galaxies have an outflow rate comparable to their star formation rate (SFR), or even higher by a factor of ~2–4, implying that starbursts can indeed be effective in removing cold gas from galaxies. Nevertheless, our results suggest that the presence of an active galactic nucleus (AGN) can boost the outflow rate by a large factor, which is found to increase with the LAGN/Lbol ratio. The gas depletion time scales due to molecular outflows are anti-correlated with the presence and luminosity of an AGN in these galaxies, and range from a few hundred million years in starburst galaxies down to just a few million years in galaxies hosting powerful AGNs. In quasar hosts, the depletion time scales due to the outflow are much shorter than the depletion time scales due to star formation. We estimate the outflow kinetic power and find that, for galaxies hosting powerful AGNs, it corresponds to about 5% of the AGN luminosity, as expected by models of AGN feedback. Moreover, we find that momentum rates of about 20 LAGN/c are common among the AGN-dominated sources in our sample. For “pure” starburst galaxies, our data tentatively support models in which outflows are mostly momentum-driven by the radiation pressure from young stars onto dusty clouds. Overall, our results indicate that, although starbursts are effective in powering massive molecular outflows, the presence of an AGN may strongly enhance such outflows, and therefore have a profound feedback effect on the evolution of galaxies by efficiently removing fuel for star formation, hence quenching star formation.
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Intensity mapping provides a unique means to probe the epoch of reionization (EoR), when the neutral intergalactic medium was ionized by energetic photons emitted from the first galaxies. The C ii ...158 m fine-structure line is typically one of the brightest emission lines of star-forming galaxies and thus a promising tracer of the global EoR star formation activity. However, C ii intensity maps at 6 z 8 are contaminated by interloping CO rotational line emission (3 ≤ Jupp ≤ 6) from lower-redshift galaxies. Here we present a strategy to remove the foreground contamination in upcoming C ii intensity mapping experiments, guided by a model of CO emission from foreground galaxies. The model is based on empirical measurements of the mean and scatter of the total infrared luminosities of galaxies at z < 3 and with stellar masses M * > 10 8 M selected in the K-band from the COSMOS/UltraVISTA survey, which can be converted to CO line strengths. For a mock field of the Tomographic Ionized-carbon Mapping Experiment, we find that masking out the "voxels" (spectral-spatial elements) containing foreground galaxies identified using an optimized CO flux threshold results in a z-dependent criterion m K AB 22 (or M * 10 9 M ) at z < 1 and makes a C ii/COtot power ratio of 10 at k = 0.1 h/Mpc achievable, at the cost of a moderate 8% loss of total survey volume.
In this first paper on the results of our Herschel PACS survey of local ultra luminous infrared galaxies (ULIRGs), as part of our SHINING survey of local galaxies, we present far-infrared ...spectroscopy of Mrk 231, the most luminous of the local ULIRGs, and a type 1 broad absorption line AGN. For the first time in a ULIRG, all observed far-infrared fine-structure lines in the PACS range were detected and all were found to be deficient relative to the far infrared luminosity by 1–2 orders of magnitude compared with lower luminosity galaxies. The deficits are similar to those for the mid-infrared lines, with the most deficient lines showing high ionization potentials. Aged starbursts may account for part of the deficits, but partial covering of the highest excitation AGN powered regions may explain the remaining line deficits. A massive molecular outflow, discovered in OH and 18OH, showing outflow velocities out to at least 1400 km s-1, is a unique signature of the clearing out of the molecular disk that formed by dissipative collapse during the merger. The outflow is characterized by extremely high ratios of 18O/16O suggestive of interstellar medium processing by advanced starbursts.
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We have detected the 158 μm C II line from 12 galaxies at z ~ 1-2. This is the first survey of this important star formation tracer at redshifts covering the epoch of maximum star formation in the ...universe and quadruples the number of reported high-z C II detections. The line is very luminous, between <0.024% and 0.65% of the far-infrared (FIR) continuum luminosity of our sources, and arises from photodissociation regions on molecular cloud surfaces. An exception is PKS 0215+015, where half of the C II emission could arise from X-ray-dominated regions near the central active galactic nucleus (AGN). The L C II/L FIR ratio in our star formation-dominated systems is ~8 times larger than that of our AGN-dominated systems. Therefore this ratio selects for star formation-dominated systems. Furthermore, the L C II/L FIR and L C II/L (CO(1-0)) ratios in our star-forming galaxies and nearby starburst galaxies are the same, so that luminous star-forming galaxies at earlier epochs (z ~ 1-2) appear to be scaled-up versions of local starbursts entailing kiloparsec-scale starbursts. Most of the FIR and C II radiation from our AGN-dominated sample (excepting PKS 0215+015) also arises from kiloparsec-scale star formation, but with far-UV radiation fields ~8 times more intense than in our star formation-dominated sample. We speculate that the onset of AGN activity stimulates large-scale star formation activity within AGN-dominated systems. This idea is supported by the relatively strong O III line emission, indicating very young stars, that was recently observed in high-z composite AGN/starburst systems. Our results confirm the utility of the C II line, and in particular, the L C II/L (FIR) and L C II/L CO(1-0) ratios as tracers of star formation in galaxies at high redshifts.
We report the detection of far-infrared (FIR) CO rotational emission from nearby active galactic nuclei (AGNs) and starburst galaxies, as well as several merging systems and Ultra-Luminous Infrared ...Galaxies (ULIRGs). Using the Herschel Photodetector Array Camera and Spectrometer (PACS), we have detected transitions in the J sub(upp) = 14-30 range. The PACS CO data obtained here provide the first reference of well-sampled FIR extragalactic CO spectral line energy distributions (SLEDs) for this range. We find a large range in the overall SLED shape, even among galaxies of similar type, demonstrating the uncertainties in relying solely on high-J CO diagnostics to characterize the excitation source of a galaxy. Combining our data with low-J line intensities taken from the literature, we present a CO ratio-ratio diagram and discuss its value in distinguishing excitation sources and physical properties of the molecular gas. The position of a galaxy on such a diagram is less a signature of its excitation mechanism, than an indicator of the presence of warm, dense molecular gas. We then quantitatively analyze the CO emission from a subset of the detected sources with single-component and two-component large velocity gradient (LVG) radiative transfer models to fit the CO SLEDs. From these fits we derive the molecular gas mass and the corresponding CO-to-H sub(2) conversion factor, alpha sub(CO), for each respective source. For the ULIRGs we find alpha values in the canonical range 0.4- 5M sub(middot in circle) (K km s super(-1) pc super(2)) super(-1), while for the other objects, alpha varies between 0.2 and 14. Finally, we compare our best-fit LVG model results with previous studies of the same galaxies and comment on any differences.
Mass outflows driven by stars and active galactic nuclei (AGNs) are a key element in many current models of galaxy evolution. They may produce the observed black-hole-galaxy mass relation and ...regulate and quench both star formation in the host galaxy and black hole accretion. However, observational evidence of such feedback processes through outflows of the bulk of the star-forming molecular gas is still scarce. Here we report the detection of massive molecular outflows, traced by the hydroxyl molecule (OH), in far-infrared spectra of ULIRGs obtained with Herschel-PACS as part of the SHINING key project. In some of these objects the (terminal) outflow velocities exceed 1000 km s--1, and their outflow rates (up to ~1200 M yr--1) are several times larger than their star formation rates. We compare the outflow signatures in different types of ULIRGs and in starburst galaxies to address the issue of the energy source (AGN or starburst) of these outflows. We report preliminary evidence that ULIRGs with a higher AGN luminosity (and higher AGN contribution to L IR) have higher terminal velocities and shorter gas depletion timescales. The outflows in the observed ULIRGs are able to expel the cold gas reservoirs from the centers of these objects within ~106-108 years.
Abstract
Line intensity mapping (LIM) provides a unique and powerful means to probe cosmic structures by measuring the aggregate line emission from all galaxies across redshift. The method is ...complementary to conventional galaxy redshift surveys that are object based and demand exquisite point-source sensitivity. The Tomographic Ionized-carbon Mapping Experiment (TIME) will measure the star formation rate during cosmic reionization by observing the redshifted C
ii
158
μ
m line (6 ≲
z
≲ 9) in the LIM regime. TIME will simultaneously study the abundance of molecular gas during the era of peak star formation by observing the rotational CO lines emitted by galaxies at 0.5 ≲
z
≲ 2. We present the modeling framework that predicts the constraining power of TIME on a number of observables, including the line luminosity function and the auto- and cross-correlation power spectra, including synergies with external galaxy tracers. Based on an optimized survey strategy and fiducial model parameters informed by existing observations, we forecast constraints on physical quantities relevant to reionization and galaxy evolution, such as the escape fraction of ionizing photons during reionization, the faint-end slope of the galaxy luminosity function at high redshift, and the cosmic molecular gas density at cosmic noon. We discuss how these constraints can advance our understanding of cosmological galaxy evolution at the two distinct cosmic epochs for TIME, starting in 2021, and how they could be improved in future phases of the experiment.
We present the results of interferometric spectral line observations of Arp 220 at 3.5 mm and 1.2 mm from the Plateau de Bure Interferometer, imaging the two nuclear disks in H super(13)CN(1-0) and ...(3-2), H super(13)CO+(1-0) and (3-2), and HN super(13)C(3-2) as well as SiO(2-1) and (6-5), HC super(15)N(3-2), and SO(6 sub(6)-5 sub(5)). The gas traced by SiO(6-5) has a complex and extended kinematic signature including a prominent P Cygni profile, almost identical to previous observations of HCO+(3-2). Spatial offsets (XT north and south of the continuum center in the emission and absorption of the SiO(6-5) P Cygni profile in the western nucleus (WN) imply a bipolar outflow, delineating the northern and southern edges of its disk and suggesting a disk radius of ~40 pc, consistent with that found by ALMA observations of Arp 220. We address the blending of SiO(6-5) and H super(13)CO+(3-2) by considering two limiting cases with regards to the H super(13)CO+ emission throughout our analysis. Large velocity gradient modeling is used to constrain the physical conditions of the gas and to infer abundance ratios in the two nuclei. Our most conservative lower limit on the H super(13)CN/H super(13)C O+ abundance ratio is 11 in the WN, compared with 0.10 in the eastern nucleus (EN). Comparing these ratios to the literature we argue on chemical grounds for an energetically significant active galactic nucleus in the WN driving either X-ray or shock chemistry, and a dominant starburst in the EN.
We report the detection of far-IR CO rotational emission from the prototypical Seyfert 2 galaxy NGC 1068. Using Herschel-PACS, we have detected 11 transitions in the J sub(upper) = 14-30 (E ...sub(upper)/k sub(B) = 580-2565 K) range, all of which are consistent with arising from within the central 10" (700 pc). The detected transitions are modeled as arising from two different components: a moderate-excitation (ME) component close to the galaxy systemic velocity and a high-excitation (HE) component that is blueshifted by ~80 km s super(-1). We employ a large velocity gradient model and derive n sub(H2) ~ 10 super(5.6) cm super(-3), T sub(kin) ~ 170 K, and M sub(H2) ~ 10 super(6.7) M sub(middot in circle) for the ME component and n sub(H2) ~ 10 super(6.4) cm super(-3), T sub(kin) ~ 570 K, and M sub(H2) ~ 10 super(5.6) M sub(middot in circle) for the HE component, although for both components the uncertainties in the density and mass are + or -(0.6-0.9) dex. Both components arise from denser and possibly warmer gas than traced by low-J CO transitions, and the ME component likely makes a significant contribution to the mass budget in the nuclear region. We compare the CO line profiles with those of other molecular tracers observed at higher spatial and spectral resolution and find that the ME transitions are consistent with these lines arising in the ~200 pc diameter ring of material traced by H sub(2) 1-0 S(1) observations. The blueshift of the HE lines may also be consistent with the bluest regions of this H sub(2) ring, but a better kinematic match is found with a clump of infalling gas ~40 pc north of the active galactic nucleus (AGN). We consider potential heating mechanisms and conclude that X-ray- or shock heating of both components is viable, while far-UV heating is unlikely. We discuss the prospects of placing the HE component near the AGN and conclude that while the moderate thermal pressure precludes an association with the ~1 pc radius H sub(2)O maser disk, the HE component could potentially be located only a few parsecs more distant from the AGN and might then provide the N sub(H) ~ 10 super(25) cm super(-2) column obscuring the nuclear hard X-rays. Finally, we also report sensitive upper limits extending up to J sub(upper) = 50, which place constraints on a previous model prediction for the CO emission from the X-ray obscuring torus.
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