We present the first results of a survey of the CII157.7 mu m emission line in 241 luminous infrared galaxies (LIRGs) comprising the Great Observatories All-sky LIRG Survey (GOALS) sample, obtained ...with the PACS instrument on board the Herschel Space Observatory. The CII luminosities, L sub(CII), of the LIRGs in GOALS range from ~10 super(7) to 2 x 10 super(9) L sub(middot in circle). We find that LIRGs show a tight correlation of CII/FIR with far-IR (FIR) flux density ratios, with a strong negative trend spanning from ~10 super(-2) to 10 super(-4), as the average temperature of dust increases. We find correlations between the CII/FIR ratio and the strength of the 9.7 mu m silicate absorption feature as well as with the luminosity surface density of the mid-IR emitting region (summationoperator sub(MIR)), suggesting that warmer, more compact starbursts have substantially smaller CII/FIR ratios. Pure star-forming LIRGs have a mean CII/FIR ~ 4 x 10 super(-3), while galaxies with low polycyclic aromatic hydrocarbon (PAH) equivalent widths (EWs), indicative of the presence of active galactic nuclei (AGNs), span the full range in CII/FIR. However, we show that even when only pure star-forming galaxies are considered, the CII/FIR ratio still drops by an order of magnitude, from 10 super(-2) to 10 super(-3), with summationoperator sub(MIR) and summationoperator sub(IR), implying that the CII157.7 mu m luminosity is not a good indicator of the star formation rate (SFR) for most local LIRGs, for it does not scale linearly with the warm dust emission most likely associated to the youngest stars. Moreover, even in LIRGs in which we detect an AGN in the mid-IR, the majority (2/3) of galaxies show CII/FIR > or =, slanted 10 super(-3) typical of high 6.2 mu m PAH EW sources, suggesting that most AGNs do not contribute significantly to the FIR emission. We provide an empirical relation between the CII/FIR and the specific SFR for star-forming LIRGs. Finally, we present predictions for the starburst size based on the observed CII and FIR luminosities which should be useful for comparing with results from future surveys of high-redshift galaxies with ALMA and CCAT.
We investigate the relationship between 8.44 GHz brightness temperatures and 1.4 to 8.44 GHz radio spectral indices with 6.2 mu m polycyclic aromatic hydrocarbon (PAH) emission and 9.7 mu m silicate ...absorption features for a sample of 36 local luminous and ultra-luminous infrared galaxies. The three active galactic nuclei (AGN) identified through their excessively large 8.44 GHz brightness temperatures are also identified as AGN via their small 6.2 mu m PAH EQWs. Finally, we investigate the location of these infrared-bright systems relative to the main sequence of star-forming galaxies in the local universe. We find that the radio spectral indices of galaxies flatten with increasing distance above the main sequence, or in other words, with increasing specific star formation rate. This indicates that galaxies located above the main sequence, having high specific star formation rates, are typically compact star-bursts hosting deeply embedded star formation that becomes more optically thick in the radio and infrared with increased distance above the main sequence.
ABSTRACT
We present new Institut de Radioastronomie Millimétrique (IRAM) 30 m spectroscopic observations of the ∼88 GHz band, including emission from the
multiplet, HCN (
,
, and
, for a sample of 58 ...local luminous and ultraluminous infrared galaxies from the Great Observatories All-sky LIRG Survey (GOALS). By combining our new IRAM data with literature data and
Spitzer
/IRS spectroscopy, we study the correspondence between these putative tracers of dense gas and the relative contribution of active galactic nuclei (AGNs) and star formation to the mid-infrared luminosity of each system. We find the HCN (1–0) emission to be enhanced in AGN-dominated systems (
/
), compared to composite and starburst-dominated systems (
/
and 0.88, respectively). However, some composite and starburst systems have
/
ratios comparable to those of AGNs, indicating that enhanced HCN emission is not uniquely associated with energetically dominant AGNs. After removing AGN-dominated systems from the sample, we find a linear relationship (within the uncertainties) between log
10
(
) and log
10
(
L
IR
), consistent with most previous findings.
/
L
IR
, typically interpreted as the dense-gas depletion time, appears to have no systematic trend with
L
IR
for our sample of luminous and ultraluminous infrared galaxies, and has significant scatter. The galaxy-integrated
and
emission do not appear to have a simple interpretation in terms of the AGN dominance or the star formation rate, and are likely determined by multiple processes, including density and radiative effects.
The Great Observatories All-Sky LIRG Survey (GOALS) is a comprehensive, multiwavelength study of luminous infrared galaxies (LIRGs) in the local universe. Here we present low resolution Spitzer ...Infrared Spectrograph spectra covering 5-38 mu m and provide a basic analysis of the mid-IR spectral properties observed for nearby LIRGs. In a companion paper, we discuss detailed fits to the spectra and compare the LIRGs to other classes of galaxies. When compared to the MIR spectra of submillimeter galaxies (SMGs) at z ~ 2, both the average GOALS LIRG and ULIRG spectra are more absorbed at 9.7 mu m and the average GOALS LIRG has more PAH emission. However, when the AGN contributions to both the local GOALS LIRGs and the high-z SMGs are removed, the average local starbursting LIRG closely resembles the starburst-dominated SMGs.
Interactions between pairs of isolated dwarf galaxies provide a critical window into low-mass hierarchical, gas-dominated galaxy assembly and the build-up of stellar mass in low-metallicity systems. ...We present the first Very Large Telescope/Multi Unit Spectroscopic Explorer (VLT/MUSE) optical integral field unit (IFU) observations of the interacting dwarf pair dm1647+21 selected from the TiNy Titans survey. The H emission is widespread and corresponds to a total unobscured star formation rate (SFR) of 0.44 M yr−1, which is 2.7 times higher than the SFR inferred from Sloan Digital Sky Survey (SDSS) data. The implied specific SFR (sSFR) for the system is elevated by more than an order of magnitude above non-interacting dwarfs in the same mass range. This increase is dominated by the lower-mass galaxy, which has a sSFR enhancement of >50. Examining the spatially resolved maps of classic optical line diagnostics, we find that the interstellar medium (ISM) excitation can be fully explained by star formation. The velocity field of the ionized gas is not consistent with simple rotation. Dynamical simulations indicate that the irregular velocity field and the stellar structure is consistent with the identification of this system as an ongoing interaction between two dwarf galaxies. The widespread, clumpy enhancements in the star formation in this system point to important differences in the effect of mergers on dwarf galaxies, compared to massive galaxies; rather than the funneling of gas to the nucleus and giving rise to a nuclear starburst, starbursts in low-mass galaxy mergers may be triggered by large-scale ISM compression, and thus may be more distributed.
We present new Karl G. Jansky Very Large Array radio continuum images of the nuclei of Arp 220, the nearest ultra-luminous infrared galaxy. These new images have both the angular resolution to study ...the detailed morphologies of the two nuclei that power the galaxy merger and sensitivity to a wide range of spatial scales. At 33 GHz, we achieve a resolution of 0.081 x 0.063 and resolve the radio emission surrounding both nuclei. We conclude from the decomposition of the radio spectral energy distribution that a majority of the 33 GHz emission is synchrotron radiation. The spatial distributions of radio emission in both nuclei are well described by exponential profiles. According to the calculations, the nuclei of Arp 220 are only transparent in the frequency range ~5-350 GHz. Our results offer no clear evidence that an active galactic nucleus dominates the emission from either nucleus at 33 GHz.
ABSTRACT We have performed a spectral decomposition to search for recoiling supermassive black holes (rSMBHs) in Sloan Digital Sky Survey (SDSS) quasi-stellar objects (QSOs) with z < 0.25. Out of ...1271 QSOs, we have identified 26 rSMBH candidates that are recoiling toward us. The projected recoil velocities range from −76 to −307 km s−1 with a mean of −149 58 km s−1. Most of the rSMBH candidates are hosted by gas-rich luminous infrared galaxies (LIRGs)/ultra-luminous infrared galaxies (ULIRGs), but only 23% of them show signs of tidal features, which suggests that a majority of them are advanced mergers. We find that the black hole masses MBH of the rSMBH candidates are on average ∼5 times smaller than those of their stationary counterparts and cause a scatter in the relation. The Eddington ratios of all of the rSMBH candidates are larger than 0.1, with a mean of 0.52 0.27, suggesting that they are actively accreting mass. Velocity shifts in high-excitation coronal lines suggest that the rSMBH candidates are recoiling with an average velocity of about −265 km s−1. The electron density in the narrow line region of the H ii rSMBH candidates is about 1/10 of that in active galactic nucleus (AGN) rSMBH candidates, probably because the AGN in the former was more spatially offset than that in the latter. The estimated spatial offsets between the rSMBH candidate and the center of the host galaxy range from 0 21 to 1 97 and need to be confirmed spatially with high-resolution adaptive optics imaging observations.
We present results from the second part of our analysis of the extended mid-infrared (MIR) emission of the GOALS sample based on 5-14 Delta *mm low-resolution spectra obtained with the Infrared ...Spectrograph on Spitzer. We calculate the fraction of extended emission (FEE) as a function of wavelength for all galaxies in the sample, FEE Delta *l, defined as the fraction of the emission that originates outside of the unresolved central component of a source, and spatially separate the MIR spectrum of a galaxy into its nuclear and extended components. We find that the Ne II12.81 Delta *mm emission line is as compact as the hot dust MIR continuum, while the polycyclic aromatic hydrocarbon (PAH) emission is more extended. In addition, the 6.2 and 7.7 Delta *mm PAH emission is more compact than that of the 11.3 Delta *mm PAH, which is consistent with the formers being enhanced in a more ionized medium. The presence of an active galactic nucleus (AGN) or a powerful nuclear starburst increases the compactness and the luminosity surface density of the hot dust MIR continuum, but has a negligible effect on the spatial extent of the PAH emission on kpc-scales. Furthermore, it appears that both processes, AGN and/or nuclear starburst, are indistinguishable in terms of how they modify the integrated PAH-to-continuum ratio of the FEE in (ultra)luminous infrared galaxies ((U)LIRGs). Globally, the 5-14 Delta *mm spectra of the extended emission component are homogeneous for all galaxies in the GOALS sample. This suggests that, independently of the spatial distribution of the various MIR features, the physical properties of star formation occurring at distances farther than 1.5 kpc from the nuclei of (U)LIRGs are very similar, resembling local star-forming galaxies with L IR < 1011 L , as well as star-formation-dominated ULIRGs at z ~ 2. In contrast, the MIR spectra of the nuclear component of local ULIRGs and LIRGs are very diverse. These results imply that the observed variety of the integrated MIR properties of local (U)LIRGs arise, on average, only from the processes that are taking place in their cores.
We present results of Hubble Space Telescope (HST) NICMOS H-band imaging of 73 of the most luminous (i.e., logL IR/L >11.4) infrared galaxies (LIRGs) in the Great Observatories All-sky LIRG Survey. ...This data set combines multi-wavelength imaging and spectroscopic data from space-based (Spitzer, HST, GALEX, and Chandra) and ground-based telescopes. In this paper, we use high-resolution near-infrared data to recover nuclear structure that is obscured by dust at optical wavelengths and measure the evolution in this structure along the merger sequence. A large fraction of all galaxies in our sample possess double nuclei (~63%) or show evidence for triple nuclei (~6%). Half of these double nuclei are not visible in the HST B-band images due to dust obscuration. The majority of interacting LIRGs have remaining merger timescales of 0.3-1.3 Gyr, based on the projected nuclear separations and the mass ratio of nuclei. We find that the bulge luminosity surface density L Bulge/R 2 Bulge increases significantly along the merger sequence (primarily due to a decrease of the bulge radius), while the bulge luminosity shows a small increase toward late merger stages. No significant increase of the bulge Sersic index is found. LIRGs that show no interaction features have on average a significantly larger bulge luminosity, suggesting that non-merging LIRGs have larger bulge masses than merging LIRGs. This may be related to the flux-limited nature of the sample and the fact that mergers can significantly boost the IR luminosity of otherwise low luminosity galaxies. We find that the projected nuclear separation is significantly smaller for ULIRGs (median value of 1.2 kpc) than for LIRGs (median value of 6.7 kpc), suggesting that the LIRG phase appears earlier in mergers than the ULIRG phase.
We present Giant Metrewave Radio Telescope H i observations and deep Canada–France–Hawaii Telescope (CFHT) MegaCam optical images of the gas-rich interacting galaxy group NGC 871/NGC 876/NGC 877 ...(hereafter NGC 871/6/7). Our high-resolution data sets provide a census of the H i and stellar properties of the detected gas-rich group members. In addition to a handful of spiral, irregular and dwarf galaxies, this group harbours an intriguing H i feature, AGC 749170, that has a gas mass of ∼109.3 M⊙, a dynamical-to-gas mass ratio of ∼1 (assuming that the cloud is rotating and in dynamical equilibrium) and no optical counterpart in previous imaging. Our observations have revealed a faint feature in the CFHT g
′ and r
′ bands; if it is physically associated with AGC 749170, the latter has
$M/L_{\rm g} >1000 \,\mathrm{M}_{{\odot }}/\mathrm{L}_{{\odot }}$
as well as a higher metallicity (estimated using photometric colours) and a significantly younger stellar population than the other low-mass gas-rich group members. These properties, as well as its spectral and spatial location with respect to its suspected parent galaxies, strongly indicate a tidal origin for AGC 749170. Overall, the H i properties of AGC 749170 resemble those of other optically dark/dim clouds that have been found in groups. These clouds could represent a class of relatively long-lived H i-rich tidal remnants that survive in intermediate-density environments.
![EXPLAINING THE [C II]157.7 ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-637X/small "EXPLAINING THE [C II]157.7 μm DEFICIT IN LUMINOUS INFRARED GALAXIES—FIRST RESULTS FROM A HERSCHEL /PACS STUDY OF THE GOALS SAMPLE")
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