Abstract
We present results from the James Webb Space Telescope Director’s Discretionary Time Early Release Science program 1328 targeting the nearby, luminous infrared galaxy, VV 114. We use the ...MIRI and NIRSpec instruments to obtain integral-field spectroscopy of the heavily obscured eastern nucleus (V114E) and surrounding regions. The spatially resolved, high-resolution spectra reveal the physical conditions in the gas and dust over a projected area of 2–3 kpc that includes the two brightest IR sources, the NE and SW cores. Our observations show for the first time spectroscopic evidence that the SW core hosts an active galactic nucleus as evidenced by its very low 6.2
μ
m and 3.3
μ
m polycyclic aromatic hydrocarbon equivalent widths (0.12 and 0.017
μ
m, respectively) and mid- and near-IR colors. Our observations of the NE core show signs of deeply embedded star formation including absorption features due to aliphatic hydrocarbons, large quantities of amorphous silicates, as well as HCN due to cool gas along the line of sight. We detect elevated Fe
ii
/Pf
α
consistent with extended shocks coincident with enhanced emission from warm H
2
, far from the IR-bright cores and clumps. We also identify broadening and multiple kinematic components in both H
2
and fine structure lines caused by outflows and previously identified tidal features.
We present the results of a Hubble Space Telescope ACS/HRC FUV, ACS/WFC optical study into the cluster populations of a sample of 22 Luminous Infrared Galaxies in the Great Observatories All-Sky LIRG ...Survey. Through integrated broadband photometry, we have derived ages and masses for a total of 484 star clusters contained within these systems. This allows us to examine the properties of star clusters found in the extreme environments of LIRGs relative to lower luminosity star-forming galaxies in the local universe. We find that by adopting a Bruzual & Charlot simple stellar population model and Salpeter initial mass function, the age distribution of the clusters declines as , consistent with the age distribution derived for the Antennae Galaxies, and interpreted as evidence for rapid cluster disruption occurring in the strong tidal fields of merging galaxies. The large number of young clusters identified in the sample also suggests that LIRGs are capable of producing more high-mass clusters than what is observed to date in any lower luminosity star-forming galaxy in the local universe. The observed cluster mass distribution of is consistent with the canonical −2 power law used to describe the underlying initial cluster mass function (ICMF) for a wide range of galactic environments. We interpret this as evidence against mass-dependent cluster disruption, which would flatten the observed CMF relative to the underlying ICMF distribution.
We apply the da Cunha et al. (2008, MNRAS, 388, 1595) model of the spectral energy distribution (SEDs) of galaxies to a small pilot sample of purely star-forming ultra-luminous infrared galaxies ...(ULIRGs). We interpret the observed SEDs of 16 ULIRGs using this physically-motivated model that accounts for both the emission of stellar populations from the ultraviolet to the near-infrared and for the attenuation by dust in two components: an optically-thick starburst component and the diffuse ISM. The infrared emission is computed by assuming that all the energy absorbed by dust in these components is re-radiated at mid- and far-infrared wavelengths. This model allows us to derive statistically physical properties including star formation rates, stellar masses, the temperatures and masses of different dust components, and plausible star formation histories. We find that, although the ultraviolet-to-near-infrared emission represents only a small fraction of the total power radiated by ULIRGs, observations in this wavelength range are important for understanding the properties of the stellar populations and dust attenuation in the diffuse ISM of these galaxies. Furthermore, our analysis indicates that the use of mid-infrared spectroscopy from the infrared spectrograph on the Spitzer Space Telescope is crucial to obtain realistic estimates of the extinction to the central energy source, mainly via the depth of the 9.7-μm silicate feature, and thus accurately constrain the total energy balance. Our findings are consistent with the notion that, in the local Universe, the physical properties of ULIRGs are fundamentally different from those of galaxies with lower infrared luminosities and that local ULIRGs are the result of merger-induced starbursts. While these are well-established ideas, we demonstrate the usefulness of our SED modelling in deriving relevant physical parameters that provide clues to the star formation mode of galaxies.
We present a full high resolution SPIRE FTS spectrum of the nearby ultraluminous infrared galaxy Mrk 231. In total 25 lines are detected, including CO J = 5–4 through J = 13–12, 7 rotational lines of ...H2O, 3 of OH+ and one line each of H2O+, CH+, and HF. We find that the excitation of the CO rotational levels up to J = 8 can be accounted for by UV radiation from star formation. However, the approximately flat luminosity distribution of the CO lines over the rotational ladder above J = 8 requires the presence of a separate source of excitation for the highest CO lines. We explore X-ray heating by the accreting supermassive black hole in Mrk 231 as a source of excitation for these lines, and find that it can reproduce the observed luminosities. We also consider a model with dense gas in a strong UV radiation field to produce the highest CO lines, but find that this model strongly overpredicts the hot dust mass in Mrk 231. Our favoured model consists of a star forming disk of radius 560 pc, containing clumps of dense gas exposed to strong UV radiation, dominating the emission of CO lines up to J = 8. X-rays from the accreting supermassive black hole in Mrk 231 dominate the excitation and chemistry of the inner disk out to a radius of 160 pc, consistent with the X-ray power of the AGN in Mrk 231. The extraordinary luminosity of the OH+ and H2O+ lines reveals the signature of X-ray driven excitation and chemistry in this region.
With the goal of investigating the degree to which the MIR emission traces the SFR, we analyze Spitzer 8 and 24 mu m data of star-forming regions in a sample of 33 nearby galaxies with available HST ...NICMOS images in the Pa alpha (1.8756 mu m) emission line. The galaxies are drawn from the SINGS sample and cover a range of morphologies and a factor similar to 10 in oxygen abundance. Published data on local low-metallicity starburst galaxies and LIRGs are also included in the analysis. Both the stellar continuum-subtracted 8 mu m emission and the 24 mu m emission correlate with the extinction-corrected Pa alpha line emission, although neither relationship is linear. Simple models of stellar populations and dust extinction and emission are able to reproduce the observed nonlinear trend of the 24 mu m emission versus number of ionizing photons, including the modest deficiency of 24 mu m emission in the low-metallicity regions, which results from a combination of decreasing dust opacity and dust temperature at low luminosities. Conversely, the trend of the 8 mu m emission as a function of the number of ionizing photons is not well reproduced by the same models. The 8 mu m emission is contributed, in larger measure than the 24 mu m emission, by dust heated by nonionizing stellar populations, in addition to the ionizing ones, in agreement with previous findings. Two SFR calibrations, one using the 24 mu m emission and the other using a combination of the 24 mu m and H alpha luminosities (Kennicutt and coworkers), are presented. No calibration is presented for the 8 mu m emission because of its significant dependence on both metallicity and environment. The calibrations presented here should be directly applicable to systems dominated by ongoing star formation.
We present AKARI 2.5–5 μm spectra of 145 local luminous infrared galaxies (LIRG; LIR ≥ 1011 L⊙) in the Great Observatories All-sky LIRG Survey (GOALS). In all of the spectra, we measure the line ...fluxes and equivalent widths (EQWs) of the polycyclic aromatic hydrocarbon (PAH) at 3.3 μm and the hydrogen recombination line Brα at 4.05 μm, with apertures matched to the slit sizes of the Spitzer low-resolution spectrograph and with an aperture covering ∼95% of the total flux in the AKARI two-dimensional (2D) spectra. The star formation rates (SFRs) derived from the Brα emission measured in the latter aperture agree well with SFRs estimated from LIR, when the dust extinction correction is adopted based on the 9.7 μm silicate absorption feature. Together with the Spitzer Infrared Spectrograph (IRS) 5.2–38 μm spectra, we are able to compare the emission of the PAH features detected at 3.3 μm and 6.2 μm. These are the two most commonly used near/mid-infrared indicators of starburst or active galactic nucleus (AGN) dominated galaxies. We find that the 3.3 μm and 6.2 μm PAH EQWs do not follow a linear correlation and at least a third of the galaxies classified as AGN-dominated sources using the 3.3 μm feature are classified as starbursts based on the 6.2 μm feature. These galaxies have a bluer continuum slope than galaxies that are indicated to be starburst-dominated by both PAH features. The bluer continuum emission suggests that their continuum is dominated by stellar emission rather than hot dust. We also find that the median Spitzer/IRS spectra of these sources are remarkably similar to the pure starburst-dominated sources indicated by high PAH EQWs in both 3.3 μm and 6.2 μm. Based on these results, we propose a revised starburst/AGN diagnostic diagram using 2–5 μm data: the 3.3 μm PAH EQW and the continuum color, Fν(4.3 μm)/Fν(2.8 μm). We use the AKARI and Spitzer spectra to examine the performance of our new starburst/AGN diagnostics and to estimate 3.3 μm PAH fluxes using the James Webb Space Telescope (JWST) photometric bands in the redshift range 0 < z < 5. Of the known PAH features and mid-infrared high ionization emission lines used as starburst/AGN indicators, only the 3.3 μm PAH feature is observable with JWST at z > 3.5, because the rest of the features at longer wavelengths fall outside the JWST wavelength coverage.
We present FIR 50-300 mu m - CO luminosity relations (i.e., log L sub(FIR) = alpha log L' sub(CO) + beta ) for the full CO rotational ladder from J = 1-0 up to J = 13-12 for a sample of 62 local (z < ...or =, slant 0.1) (Ultra) Luminous Infrared Galaxies (LIRGs; L sub(IR8-1000) mu m < 10 super(11) L sub(middot in circle)) using data from Herschel SPIRE-FTS and ground-based telescopes. We extend our sample to high redshifts (z > 1) by including 35 submillimeter selected dusty star forming galaxies from the literature with robust CO observations, and sufficiently well-sampled FIR/submillimeter spectral energy distributions (SEDs), so that accurate FIR luminosities can be determined. This new data set (both in terms of IR luminosity and J-ladder) reveals linear FIR - CO luminosity relations (i.e., alpha Asymptotically = to 1) for J = 1-0 up to J = 5-4, with a nearly constant normalization ( beta ~ 2).
GOALS: The Great Observatories All-Sky LIRG Survey Armus, L.; Mazzarella, J. M.; Evans, A. S. ...
Publications of the Astronomical Society of the Pacific,
06/2009, Volume:
121, Issue:
880
Journal Article
Peer reviewed
Open access
The Great Observatories All-Sky LIRG Survey (GOALS20) combines data from NASA’sSpitzer Space Telescope,
Chandra X-Ray Observatory,
Hubble Space Telescope(HST), andGalaxy Evolution Explorer(GALEX) ...observatories, together with ground-based data, into a comprehensive imaging and spectroscopic survey of over 200 low-redshift (
z < 0.088
z
<
0.088
), Luminous Infrared Galaxies (LIRGs). The LIRGs are a complete subset of theIRASRevised Bright Galaxy Sample (RBGS), which comprises 629 extragalactic objects with 60 μm flux densities above 5.24 Jy, and Galactic latitudes above five degrees. The LIRGs targeted in GOALS span the full range of nuclear spectral types defined via traditional optical line-ratio diagrams (type-1 and type-2 AGN, LINERs, and starbursts) as well as interaction stages (major mergers, minor mergers, and isolated galaxies). They provide an unbiased picture of the processes responsible for enhanced infrared emission in galaxies in the local Universe. As an example of the analytic power of the multiwavelength GOALS data set, we presentSpitzer, Chandra, HST,andGALEXimages and spectra for the interacting system VV 340 (IRAS
F14547 + 2449
F
14547
+
2449
). TheSpitzerMIPS imaging data indicates that between 80–95% of the total far-infrared emission (or about5 × 1011 L
⊙
5
×
10
11
L
⊙
) originates in VV 340 north. While theSpitzerIRAC colors of VV 340 north and south are consistent with star-forming galaxies, both theSpitzerIRS andChandraACIS data indicate the presence of an AGN in VV 340 north. The observed line fluxes, without correction for extinction, imply that the AGN accounts for less than 10%–20% of the observed infrared emission. The X-ray data are consistent with a heavily absorbed (
N
H
≥1024 cm-2
N
H
≥
10
24
cm
-
2
) AGN. The GALEX far and near-UV fluxes imply a extremely large infrared “excess” (IRX) for the system (FIR/Ffuv ∼ 81
F
IR
/
F
fuv
∼
81
) which is well above the correlation seen in starburst galaxies. Most of this excess is driven by VV 340 N, which has an IR excess of nearly 400. The VV 340 system seems to be comprised of two very different galaxies: an infrared luminous edge-on galaxy (VV 340 north) that dominates the long-wavelength emission from the system, which hosts a buried AGN; and a face-on starburst (VV 340 south) that dominates the short-wavelength emission.
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 the results of a ...multi-component, spectral decomposition analysis of the low-resolution mid-infrared (MIR) Spitzer Infrared Spectrograph spectra from 5-38 mu m of 244 LIRG nuclei. The detailed fits and high-quality spectra allow for characterization of the individual polycyclic aromatic hydrocarbon (PAH) features, warm molecular hydrogen emission, and optical depths for both silicate dust grains and water ices. We detect crystalline silicate features in ~6% of the sample but only in the most obscure sources (s sub(9.7) mu m < -1.24). While star formation appears to be the dominant process responsible for exciting the H sub(2) in most of the GOALS galaxies, a subset of LIRGs (~10%) shows excess H sub(2) emission that is inconsistent with PDR models and may be excited by shocks or AGN-induced outflows.
Using a spectral decomposition technique, we investigate the physical origin of the high-velocity emission-line gas in a sample of 39 gas-rich, ultraluminous infrared galaxy mergers. Regions with ...shock-like excitation were identified in two kinematically distinct regimes, characterized by broad (sigma > 150 km s super(-1)) and narrow linewidths (sigma < or =, slant 150 km s super(-1)). Here, we investigate the physical origin of the broad emission, which we show is predominantly excited by shocks with velocities of 200-300 km s super(-1). Considering the large amount of extinction in these galaxies, the blueshift of the broad emission suggests an origin on the near side of the galaxy and therefore an interpretation as a galactic outflow. The large spatial extent of the broad, shocked emission component is generally inconsistent with an origin in the narrow-line region of an active galactic nucleus. The kinetic energy in the mass loss as well as the luminosity of the emission lines is consistent with the fraction of the supernova energy attributed to these mechanisms by shocked stellar winds. Since some shocks can be recognized in moderately high resolution, integrated spectra of nearby ultraluminous starbursts, the spectral fitting technique introduced in Soto & Martin may therefore be used to improve the accuracy of the physical properties measured for high-redshift galaxies from their (observed frame) infrared spectra.
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