Abstract
Nuclear rings are excellent laboratories for studying intense star formation. We present results from a study of nuclear star-forming rings in five nearby normal galaxies from the Star ...Formation in Radio Survey (SFRS) and four local LIRGs from the Great Observatories All-sky LIRG Survey at sub-kiloparsec resolutions using Very Large Array high-frequency radio continuum observations. We find that nuclear ring star formation (NRSF) contributes 49%–60% of the total star formation of the LIRGs, compared to 7%–40% for the normal galaxies. We characterize a total of 57 individual star-forming regions in these rings, and find that with measured sizes of 10–200 pc, NRSF regions in the LIRGs have star formation rate (SFR) and Σ
SFR
up to 1.7
M
⊙
yr
−1
and 402
M
⊙
yr
−1
kpc
−2
, respectively, which are about 10 times higher than in NRSF regions in the normal galaxies with similar sizes, and comparable to lensed high-
z
star-forming regions. At ∼100–300 pc scales, we estimate low contributions (<50%) of thermal free–free emission to total radio continuum emission at 33 GHz in the NRSF regions in the LIRGs, but large variations possibly exist at smaller physical scales. Finally, using archival sub-kiloparsec resolution CO (
J
= 1–0) data of nuclear rings in the normal galaxies and NGC 7469 (LIRG), we find a large scatter in gas depletion times at similar molecular gas surface densities, which tentatively points to a multimodal star formation relation on sub-kiloparsec scales.
We present new Atacama Large Millimeter/submillimeter Array Band 7 (∼340 GHz) observations of the dense gas tracers HCN, HCO+, and CS in the local, single-nucleus, ultraluminous infrared galaxy IRAS ...13120-5453. We find centrally enhanced HCN (4-3) emission, relative to HCO+ (4-3), but do not find evidence for radiative pumping of HCN. Considering the size of the starburst (0.5 kpc) and the estimated supernovae rate of ∼1.2 yr−1, the high HCN/HCO+ ratio can be explained by an enhanced HCN abundance as a result of mechanical heating by the supernovae, though the active galactic nucleus and winds may also contribute additional mechanical heating. The starburst size implies a high IR of 4.7 × 1012 L kpc−2, slightly below predictions of radiation-pressure limited starbursts. The HCN line profile has low-level wings, which we tentatively interpret as evidence for outflowing dense molecular gas. However, the dense molecular outflow seen in the HCN line wings is unlikely to escape the Galaxy and is destined to return to the nucleus and fuel future star formation. We also present modeling of Herschel observations of the H2O lines and find a nuclear dust temperature of ∼40 K. IRAS 13120-5453 has a lower dust temperature and IR than is inferred for the systems termed "compact obscured nuclei (CONs)" (such as Arp 220 and Mrk 231). If IRAS 13120-5453 has undergone a CON phase, we are likely witnessing it at a time when the feedback has already inflated the nuclear ISM and diluted star formation in the starburst/active galactic nucleus core.
We present 33 GHz photometry of 103 galaxy nuclei and extranuclear star-forming complexes taken with the Green Bank Telescope as part of the Star Formation in Radio Survey. Among the sources without ...evidence for an active galactic nucleus, and also having lower frequency radio data, we find a median thermal fraction at 33 GHz of approximately 76% with a dispersion of approximately 24%. For all sources resolved on scales lap0.5 kpc, the thermal fraction is even larger, being gap90%. This suggests that the rest-frame 33 GHz emission provides a sensitive measure of the ionizing photon rate from young star-forming regions, thus making it a robust star formation rate (SFR) indicator. Comparing the 33 GHz to total IR flux ratios as a function of the radio spectral index, measured between 1.7 and 33 GHz, we find that the ratio increases as the radio spectral index flattens which does not appear to be a distance effect.
The physical state of interstellar gas and dust is dependent on the processes which heat and cool this medium. To probe heating and cooling of the interstellar medium over a large range of infrared ...surface brightness, on sub-kiloparsec scales, we employ line maps of CII 158 mu m, OI 63 mu m, and NII 122 mu m in NGC 1097 and NGC 4559, obtained with the Photodetector Array Camera & Spectrometer on board Herschel. We matched new observations to existing Spitzer Infrared Spectrograph data that trace the total emission of polycyclic aromatic hydrocarbons (PAHs). We confirm at small scales in these galaxies that the canonical measure of photoelectric heating efficiency, (CII + OI)/TIR, decreases as the far-infrared (far-IR) color, nufunctionof sub(nu)(70 mu m) nufunctionof sub(nu)(100 mu m), increases. In contrast, the ratio of far-IR cooling to total PAH emission, (CII + OI)/PAH, is a near constant ~6% over a wide range of far-IR color, 0.5 < nufunctionof sub(nu)(70 mu m) nufunctionof sub(nu)(100 mu m) <, ~0.95. In the warmest regions, where nufunctionof sub(nu)(70 mu m) nufunctionof sub(nu)(100 mu m) > ~0.95, the ratio (CII + OII)/PAH drops rapidly to 4%. We derived representative values of the local ultraviolet radiation density, G sub(0), and the gas density, n sub(H), by comparing our observations to models of photodissociation regions. The ratio G sub(0)/n sub(H), derived from fine-structure lines, is found to correlate with the mean dust-weighted starlight intensity, left angle bracketUright angle bracket, derived from models of the IR spectral energy distribution. Emission from regions that exhibit a line deficit is characterized by an intense radiation field, indicating that small grains are susceptible to ionization effects. We note that there is a shift in the 7.7/11.3 mu m PAH ratio in regions that exhibit a deficit in (CII + OI)/PAH, suggesting that small grains are ionized in these environments.
We present high spatial resolution, integral field spectrograph (IFS) observations of the nearby low-ionization nuclear emission-line region (LINER) galaxy NGC 404 at 1.25 m (J band) and 2.2 m (K ...band) near-infrared (NIR) wavelengths. Although NGC 404 is thought to host an intermediate-mass black hole (BH) at its center, it has been unclear whether accretion onto the BH or another mechanism such as shock excitation drives its LINER emission at optical/NIR wavelengths. We use the OSIRIS IFS at Keck Observatory behind laser guide star adaptive optics to map the strength and kinematics of Fe ii, H2, and hydrogen recombination lines at spatial resolutions of 1 pc across the central 30 pc of the galaxy. The H2 gas is in a central rotating disk, and ratios of multiple H2 lines indicate that the molecular gas is thermally excited, with some contribution from UV fluorescence. The Fe ii emission is more extended and diffuse than the molecular gas and has a different kinematic structure that reaches higher velocities/dispersions. We also map the strength of the CO stellar absorption feature and constrain the dominant age of the nuclear stellar population to ∼1 Gyr. Finally, we find regions across the nucleus of NGC 404 with Fe ii/Paβ line ratios up to 6.5, ∼2.5 times higher than the ratio measured from spatially integrated spectra. From these high line ratios, we conclude that shocks are the dominant physical mechanism exciting NGC 404's LINER emission and argue that a possible source of this shock excitation is a supernova remnant.
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.
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.
We present an update to the ultraviolet-to-radio database of global broadband photometry for the 79 nearby galaxies that comprise the union of the KINGFISH (Key Insights on Nearby Galaxies: A ...Far-Infrared Survey with Herschel) and SINGS (Spitzer Infrared Nearby Galaxies Survey) samples. The 34-band data set presented here includes contributions from observational work carried out with a variety of facilities including GALEX, SDSS, Pan-STARRS1, NOAO, 2MASS, Wide-Field Infrared Survey Explorer, Spitzer, Herschel, Planck, JCMT, and the VLA. Improvements of note include recalibrations of previously published SINGS BVRCIC and KINGFISH far-infrared/submillimeter photometry. Similar to previous results in the literature, an excess of submillimeter emission above model predictions is seen primarily for low-metallicity dwarf or irregular galaxies. This 33-band photometric data set for the combined KINGFISH+SINGS sample serves as an important multiwavelength reference for the variety of galaxies observed at low redshift. A thorough analysis of the observed spectral energy distributions is carried out in a companion paper.
ABSTRACT The H i and CO components of the interstellar medium (ISM) are usually used to derive the dynamical mass of nearby galaxies. Both components become too faint to be used as a tracer in ...observations of high-redshift galaxies. In those cases, the 158 m line of atomic carbon (C ii) may be the only way to derive . As the distribution and kinematics of the ISM tracer affects the determination of , it is important to quantify the relative distributions of H i, CO, and C ii. H i and CO are well-characterized observationally, however, for C ii only very few measurements exist. Here we compare observations of CO, H i, and C ii emission of a sample of nearby galaxies, drawn from the HERACLES, THINGS, and KINGFISH surveys. We find that within R25, the average C ii exponential radial profile is slightly shallower than that of the CO, but much steeper than the H i distribution. This is also reflected in the integrated spectrum ("global profile"), where the C ii spectrum looks more like that of the CO than that of the H i. For one galaxy, a spectrally resolved comparison of integrated spectra was possible; other comparisons were limited by the intrinsic line-widths of the galaxies and the coarse velocity resolution of the C ii data. Using high-spectral-resolution SOFIA C ii data of a number of star forming regions in two nearby galaxies, we find that their C ii linewidths agree better with those of the CO than the H i. As the radial extent of a given ISM tracer is a key input in deriving from spatially unresolved data, we conclude that the relevant length-scale to use in determining based on C ii data, is that of the well-characterized CO distribution. This length scale is similar to that of the optical disk.
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![COMPARING [C ii], H i, AND ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-6256_1538-3881/small "COMPARING [C ii], H i, AND CO DYNAMICS OF NEARBY GALAXIES")