-
S. Stierwalt,
L. Armus,
J. A. Surace,
H. Inami,
A. O. Petric,
T. Diaz-Santos,
S. Haan,
V. Charmandaris,
J. Howell,
D. C. Kim, [......],
S. Lord,
B. F. Madore,
J. E. Melbourne,
E. J. Murphy,
J. A. Rich,
B. Schulz,
E. Sturm,
V. U,
T. Vavilkin,
K. Xu
[show abstract]
[hide abstract]
ABSTRACT: The Great Observatories All-Sky LIRG Survey (GOALS) is a multiwavelength
study of luminous infrared galaxies (LIRGs) in the local universe. Here we
present low resolution Spitzer spectra covering 5-38um and provide a basic
analysis of the mid-IR spectral properties for nearby LIRGs. In a companion
paper, we discuss detailed fits to the spectra. The GOALS sample of 244 nuclei
in 180 luminous and 22 ultraluminous IR galaxies represents a complete subset
of the IRAS RBGS and covers a range of merger stages, morphologies and spectral
types. The majority (>60%) of GOALS LIRGs have high 6.2um PAH equivalent widths
(EQW > 0.4um) and low levels of silicate absorption (s_9.7um >-1.0). There is a
general trend among the U/LIRGs for silicate depth and MIR slope to increase
with LIR. U/LIRGs in the late stages of a merger also have on average steeper
MIR slopes and higher levels of dust obscuration. Together these trends suggest
that as gas & dust is funneled towards the center of a coalescing merger, the
nuclei become more compact and obscured. The sources that depart from these
correlations have very low PAH EQW (EQW < 0.1um) consistent with their MIR
emission being dominated by an AGN. The most heavily dust obscured sources are
the most compact in their MIR emission, suggesting that the obscuring (cool)
dust is associated with the outer regions of the starburst. As the merger
progresses a marked decline is seen for the fraction of high EQW (star
formation dominated) sources while the fraction of composite sources increases
but the fraction of AGN-dominated sources remains low. When compared to the MIR
spectra of submillimeter galaxies (SMGs) at z~2, the average GOALS LIRG is more
absorbed at 9.7um and has more PAH emission. However, when the AGN
contributions to both the local LIRGs and the high-z SMGs are removed, the
average local starbursting LIRG closely resembles the starbursting SMGs.
02/2013;
-
J. M. Mazzarella,
K. Iwasawa,
T. Vavilkin,
L. Armus,
D. -C. Kim,
G. Bothun,
A. S. Evans, H. W. W. Spoon,
S. Haan,
J. H. Howell, [......],
P. Appleton,
B. H. P. Chan,
D. T. Frayer,
H. Inami,
E. Ye. Khachikian,
B. F. Madore,
G. C. Privon,
E. Sturm,
Vivian U,
S. Veilleux
[show abstract]
[hide abstract]
ABSTRACT: Results of observations with the Spitzer, Hubble, GALEX, Chandra, and
XMM-Newton space telescopes are presented for the Luminous Infrared Galaxy
(LIRG) merger Mrk 266. The SW (Seyfert 2) and NE (LINER) nuclei reside in
galaxies with Hubble types SBb (pec) and S0/a (pec), respectively. Both
galaxies have L > L*, and they are inferred to each contain a ~2.5x10^8 M_sun
black hole. Mrk 266 SW is likely the primary source of a bright Fe K-alpha line
detected from the system, consistent with the reflection-dominated X-ray
spectrum of a heavily obscured AGN. Optical knots embedded in an arc with
aligned radio continuum radiation, combined with luminous H_2 line emission,
provide evidence for a radiative bow shock in an AGN-driven outflow surrounding
the NE nucleus. Soft X-ray emission modeled as shock-heated plasma is
co-spatial with radio continuum emission between the galaxies. Mid-IR
diagnostics indicate roughly equal contributions of AGN and starburst radiation
powering the bolometric luminosity. Approximately 120 star clusters have been
detected, with most having estimated ages < 50 Myr. Detection of 24 micron
emission extending ~34 arcsec (20 kpc) north of the galaxies is interpreted as
~2x10^7 M_sun of dust entrained in an outflowing superwind; at optical
wavelengths this region is resolved into a fragmented morphology indicative of
Rayleigh-Taylor instabilities in an expanding shell of ionized gas. Mrk 266
demonstrates that the dust "blow-out" phase can begin in a LIRG well before the
galaxies fully coalesce during a subsequent ULIRG phase, and rapid gas
consumption in luminous dual AGNs (kpc scale separations) early in the merger
process may explain the paucity of detected binary QSOs (sub-pc scale orbits)
in large surveys. An evolutionary sequence is proposed representing a
progression from dual to binary AGNs, accompanied by an increase in observed
L_x/L_ir ratios by 10^4 or more.
08/2012;
-
F. Modica,
T. Vavilkin,
A. S. Evans,
D. -C. Kim,
J. M. Mazzarella,
K. Iwasawa,
A. Petric,
J. H. Howell,
J. A. Surace,
L. Armus, H. W. W. Spoon,
D. B. Sanders,
J. E. Barnes
[show abstract]
[hide abstract]
ABSTRACT: New optical HST, Spitzer, GALEX, and Chandra observations of the
single-nucleus, luminous infrared galaxy (LIRG) merger IC 883 are presented.
The galaxy is a member of the Great Observatories All-sky LIRG Survey (GOALS),
and is of particular interest for a detailed examination of a luminous
late-stage merger due to the richness of the optically-visible star clusters
and the extended nature of the nuclear X-ray, mid-IR, CO and radio emission. In
the HST ACS images, the galaxy is shown to contain 156 optically visible star
clusters distributed throughout the nuclear regions and tidal tails of the
merger, with a majority of visible clusters residing in an arc ~ 3-7 kpc from
the position of the mid-infrared core of the galaxy. The luminosity functions
of the clusters have an alpha_F435W ~ -2.17+/-0.22 and alpha_F814W ~
-2.01+/-0.21. Further, the colors and absolute magnitudes of the majority of
the clusters are consistent with instantaneous burst population synthesis model
ages in the range of a few x10^7 - 10^8 yrs (for 10^5 M_sun clusters), but may
be as low as few x10^6 yrs with extinction factored in. The X-ray and mid-IR
spectroscopy are indicative of predominantly starburst-produced nuclear
emission, and the star formation rate is ~ 80 M_sun / yr. The kinematics of the
CO emission and the morphology of both the CO and radio emission are consistent
with the nuclear starburst being situated in a highly inclined disk 2 kpc in
diameter with an infrared surface brightness mu_IR ~ 2x10^11 L_sun kpc^-2, a
factor of 10 less than that of the Orion star-forming region. Finally, the
detection of the [Ne V] 14.32 um emission line is evidence that an AGN is
present. The faintness of the line (i.e., [Ne V] / [Ne II] um ~ 0.01) and the
small equivalent width of the 6.2 um PAH feature ($= 0.39\mu$m) are both
indicative of a relatively weak AGN. (abridged)
11/2011;
-
E. González-Alfonso,
J. Fischer,
J. Graciá-Carpio,
E. Sturm,
S. Hailey-Dunsheath,
D. Lutz,
A. Poglitsch,
A. Contursi,
H. Feuchtgruber,
S. Veilleux, H. W. W. Spoon,
A. Verma,
N. Christopher,
R. Davies,
A. Sternberg,
R. Genzel,
L. Tacconi
[show abstract]
[hide abstract]
ABSTRACT: Herschel/PACS spectroscopy of the luminous infrared galaxies NGC4418 and
Arp220 reveals high excitation in H2O, OH, HCN, and NH3. In NGC4418, absorption
lines were detected with E_low>800 K (H2O), 600 K (OH), 1075 K (HCN), and 600 K
(NH3), while in Arp220 the excitation is somewhat lower. While outflow
signatures in moderate excitation lines are seen in Arp220 as reported in
previous studies, in NGC4418 the lines tracing its outer regions are redshifted
relative to the nucleus, suggesting an inflow with Mdot<~12 Msun yr^{-1}. Both
galaxies have warm (Tdust>~100 K) nuclear continuum components, together with a
more extended component that is much more prominent and massive in Arp220. A
chemical dichotomy is found in both sources: on the one hand, the nuclear
regions have high H2O abundances, ~10^{-5}, and high HCN/H2O and HCN/NH3 column
density ratios of 0.1-0.4 and 2-5, respectively, indicating a chemistry typical
of evolved hot cores where grain mantle evaporation has occurred. On the other
hand, the high OH abundance, with OH/H2O ratios of ~0.5, indicates the effects
of X-rays and/or cosmic rays. The nuclear media have surface brightnesses
>~10^{13} Lsun/kpc^2 and are estimated to be thick (N_H>~10^{25} cm^{-2}).
While NGC4418 shows weak absorption in H2^{18}O and ^{18}OH, with a
^{16}O-to-^{18}O ratio of >~250-500, the strong absorption of the rare
isotopologues in Arp220 indicates ^{16}O-to-^{18}O of 70-130. Further away from
the nuclear regions, the H2O abundance decreases to <~10^{-7} and the OH/H2O
ratio is 2.5-10. Despite the different scales of NGC4418, Arp220, and Mrk231,
preliminary evidence is found for an evolutionary sequence from infall,
hot-core like chemistry, and solar oxygen isotope ratio to high velocity
outflow, disruption of the hot core chemistry and cumulative high mass stellar
processing of 18O.
09/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: We present the spectral atlas of sources observed in low resolution with the Infrared Spectrograph on board the Spitzer Space Telescope. More than 11,000 distinct sources were extracted using a dedicated algorithm based on the SMART software with an optimal extraction (AdOpt package). These correspond to all 13,000 low-resolution observations of fixed objects (both single source and cluster observations). The pipeline includes image cleaning, individual exposure combination, and background subtraction. Particular attention is given to bad pixel and outlier rejection at the image and spectra levels. Most sources are spatially unresolved so that optimal extraction reaches the highest possible signal-to-noise ratio. For all sources, an alternative extraction is also provided that accounts for all of the source flux within the aperture. CASSIS provides publishable quality spectra through an online database together with several important diagnostics, such as the source spatial extent and a quantitative measure of detection level. Ancillary data such as available spectroscopic redshifts are also provided. The database interface will eventually provide various ways to interact with the spectra, such as on-the-fly measurements of spectral features or comparisons among spectra.
The Astrophysical Journal Supplement Series 08/2011; 196(1):8. · 13.46 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present the spectral atlas of sources observed in low resolution with the
Infrared Spectrograph on board the Spitzer Space Telescope. More than 11,000
distinct sources were extracted using a dedicated algorithm based on the SMART
software with an optimal extraction (AdOpt package). These correspond to all
13,000 low resolution observations of fixed objects (both single source and
cluster observations). The pipeline includes image cleaning, individual
exposure combination, and background subtraction. A particular attention is
given to bad pixel and outlier rejection at the image and spectra levels. Most
sources are spatially unresolved so that optimal extraction reaches the highest
possible signal-to-noise ratio. For all sources, an alternative extraction is
also provided that accounts for all of the source flux within the aperture.
CASSIS provides publishable quality spectra through an online database together
with several important diagnostics, such as the source spatial extent and a
quantitative measure of detection level. Ancillary data such as available
spectroscopic redshifts are also provided. The database interface will
eventually provide various ways to interact with the spectra, such as
on-the-fly measurements of spectral features or comparisons among spectra.
08/2011;
-
F. Costagliola,
S. Aalto,
M. I. Rodriguez,
S. Muller, H. W. W. Spoon,
S. Martín,
M. A. Peréz-Torres,
A. Alberdi,
J. E. Lindberg,
F. Batejat,
E. Jütte,
P. van der Werf,
F. Lahuis
[show abstract]
[hide abstract]
ABSTRACT: We investigate the molecular gas properties of a sample of 23 galaxies in
order to find and test chemical signatures of galaxy evolution and to compare
them to IR evolutionary tracers. Observation at 3 mm wavelengths were obtained
with the EMIR broadband receiver, mounted on the IRAM 30 m telescope on Pico
Veleta, Spain. We compare the emission of the main molecular species with
existing models of chemical evolution by means of line intensity ratios
diagrams and principal component analysis. We detect molecular emission in 19
galaxies in two 8 GHz-wide bands centred at 88 and 112 GHz. The main detected
transitions are the J=1-0 lines of CO, 13CO, HCN, HNC, HCO+, CN, and C2H. We
also detect HC3N J=10-9 in the galaxies IRAS 17208, IC 860, NGC 4418, NGC 7771,
and NGC 1068. The only HC3N detections are in objects with HCO+/HCN<1 and warm
IRAS colours. Galaxies with the highest HC3N/HCN ratios have warm IRAS colours
(60/100 {\mu}m>0.8). The brightest HC3N emission is found in IC 860, where we
also detect the molecule in its vibrationally excited state.We find low HNC/HCN
line ratios (<0.5), that cannot be explained by existing PDR or XDR chemical
models. Bright HC3N emission in HCO+-faint objects may imply that these are not
dominated by X-ray chemistry. Thus the HCN/HCO+ line ratio is not, by itself, a
reliable tracer of XDRs. Bright HC3N and faint HCO+ could be signatures of
embedded starformation, instead of AGN activity.
01/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: We present mid-infrared (mid-IR) spectra of six FeLoBAL quasi-stellar objects (QSOs) at 1 < z < 1.8, taken with the Spitzer Space Telescope. The spectra span a range of shapes, from hot dust-dominated active galactic nuclei (AGNs) with silicate emission at 9.7 μm to moderately obscured starbursts with strong polycyclic aromatic hydrocarbon (PAH) emission. The spectrum of one object, SDSS 1214–0001, shows the most prominent PAHs yet seen in any QSO at any redshift, implying that the starburst dominates the mid-IR emission with an associated star formation rate on the order of 2700 M ☉ yr–1. With the caveats that our sample is small and not robustly selected, we combine our mid-IR spectral diagnostics with previous observations to propose that FeLoBAL QSOs are at least largely comprised of systems in which (1) a merger-driven starburst is ending, (2) a luminous AGN is in the last stages of burning through its surrounding dust, and (3) we may be viewing over a restricted line-of-sight range.
The Astrophysical Journal 06/2010; 717(2):868. · 6.02 Impact Factor
-
D. Fadda,
L Yan,
G. Lagache,
A. Sajina,
D. Lutz,
S. Wuyts,
D. T. Frayer,
D. Marcillac,
E. Le Floc'h,
K. Caputi, H. W. W. Spoon,
S. Veilleux,
A. Blain,
G. Helou
[show abstract]
[hide abstract]
ABSTRACT: We present ultra-deep mid-IR spectra of 48 infrared-luminous galaxies in the GOODS-South field obtained with the InfraRed Spectrograph (IRS) on the Spitzer Space Telescope. These galaxies are selected among faint infrared sources (0.14 - 0.5 mJy at 24 um) in two redshift bins (0.76-1.05 and 1.75-2.4) to sample the major contributors to the cosmic infrared background at the most active epochs. We estimate redshifts for 92% of the sample using PAH and Si absorption features. Only few of these galaxies (5% at z~1 and 12% at z~2) have their total infrared luminosity dominated by emission from AGN. The averaged mid-IR spectra of the z~1 LIRGs and of the z~2 ULIRGs are very similar to the averaged spectrum of local starbursts and HII-like ULIRGs, respectively. We find that 6.2um PAH equivalent widths reach a plateau of ~1 um for L(24 mu) < 1E11 L(sun). At higher luminosities, EW (6.2 mu) anti-correlates with L(24 um). Intriguingly, high-z ULIRGs and SMG lie above the local EW (6.2 um) - L(24 um) relationship suggesting that, at a given luminosity, high-z ULIRGs have AGN contributions to their dust emission lower than those of local counterparts. A quantitative analysis of their morphology shows that most of the luminous IR galaxies have morphologies similar to those of IR-quiet galaxies at the same redshift. All z~2 ULIRGs of our sample are IR-excess BzK galaxies and most of them have L(FIR)/L(1600A) ratios higher than those of starburst galaxies at a given UV slope. The ``IR excess'' (Daddi et al. 2007) is mostly due to strong 7.7 um PAH emission and under-estimation of UV dust extinction. On the basis of the AGN-powered L (6 um) continuum measured directly from the mid-IR spectra, we estimate an average intrinsic X-ray AGN luminosity of L(2-10 keV) = (0.1 +/- 0.6) 1E43 erg/s, a value substantially lower than the prediction by Daddi et al. (2007). Comment: 45 pages, 36 figures, 2 tables, accepted for publication on ApJ
06/2010;
-
Hanae Inami,
L. Armus,
J. A. Surace,
J. M. Mazzarella,
A. S. Evans,
D. B. Sanders,
J. H. Howell,
A. Petric,
T. Vavilkin,
K. Iwasawa, [......],
J. A. Marshall,
H. Matsuhara,
J. E. Melbourne,
J. Rich,
B. Schulz, H. W. W. Spoon,
E. Sturm,
V. U,
S. Veilleux,
K Xu
[show abstract]
[hide abstract]
ABSTRACT: An analysis of data from the Spitzer Space Telescope, Hubble Space Telescope, Chandra X-ray Observatory, and AKARI Infrared Astronomy Satellite is presented for the z=0.036 merging galaxy system II Zw 096 (CGCG 448-020). Because II Zw 096 has an infrared luminosity of log(L_IR/L_sun) = 11.94, it is classified as a Luminous Infrared Galaxy (LIRG), and was observed as part of the Great Observatories All-sky LIRG Survey (GOALS). The Spitzer data suggest that 80% of the total infrared luminosity comes from an extremely compact, red source not associated with the nuclei of the merging galaxies. The Spitzer mid-infrared spectra indicate no high-ionization lines from a buried active galactic nucleus in this source. The strong detection of the 3.3 micron and 6.2 micron PAH emission features in the AKARI and Spitzer spectra also implies that the energy source of II Zw 096 is a starburst. Based on Spitzer infrared imaging and AKARI near-infrared spectroscopy, the star formation rate is estimated to be 120 M_sun/yr and > 45 M_sun/yr, respectively. Finally, the high-resolution B, I, and H-band images show many star clusters in the interacting system. The colors of these clusters suggest at least two populations - one with an age of 1-5 Myr and one with an age of 20-500 Myr, reddened by 0-2 magnitudes of visual extinction. The masses of these clusters span a range between 10^6-10^8 M_sun. This starburst source is reminiscent of the extra-nuclear starburst seen in NGC 4038/9 (the Antennae Galaxies) and Arp 299 but approximately an order of magnitude more luminous than the Antennae. The source is remarkable in that the off-nuclear infrared luminosity dominates the enitre system. Comment: 46 pages, 10 figures, accepted for publication in AJ
04/2010;
-
J. Bernard-Salas, H. W. W. Spoon,
V. Charmandaris,
V. Lebouteiller,
D. Farrah,
D. Devost,
B. R. Brandl,
Yanling Wu,
L. Armus,
L. Hao,
G. C. Sloan,
D. Weedman,
and J. R. Houck
[show abstract]
[hide abstract]
ABSTRACT: We present an atlas of Spitzer/IRS high-resolution (R ~ 600) 10-37 μm spectra for 24 well known starburst galaxies. The spectra are dominated by fine-structure lines, molecular hydrogen lines, and emission bands of polycyclic aromatic hydrocarbons (PAHs). Six out of the eight objects with a known active galactic nucleus (AGN) component show emission of the high excitation [Ne V] line. This line is also seen in one other object (NGC 4194) with, a priori, no known AGN component. In addition to strong PAH emission features in this wavelength range (11.3, 12.7, 16.4 μm), the spectra reveal other weak hydrocarbon features at 10.6, 13.5, 14.2 μm, and a previously unreported emission feature at 10.75 μm. An unidentified absorption feature at 13.7 μm is detected in many of the starbursts. We use the fine-structure lines to derive the abundance of neon and sulfur for 14 objects where the H I 7-6 line is detected. We further use the molecular hydrogen lines to sample the properties of the warm molecular gas. Several basic diagrams characterizing the properties of the sample are also shown. We have combined the spectra of all the pure starburst objects to create a high signal-to-noise ratio template, which is available to the community.
The Astrophysical Journal Supplement Series 09/2009; 184(2):230. · 13.46 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present an analysis of the mid-infrared emission lines for a sample of 12 low metallicity Blue Compact Dwarf (BCD) galaxies based on high resolution observations obtained with Infrared Spectrograph on board the {\rm Spitzer} Space Telescope. We compare our sample with a local sample of typical starburst galaxies and active galactic nuclei (AGNs), to study the ionization field of starbursts over a broad range of physical parameters and examine its difference from the one produced by AGN. The high-ionization line [OIV]25.89$\mu$m is detected in most of the BCDs, starbursts, and AGNs in our sample. We propose a diagnostic diagram of the line ratios [OIV]25.89$\mu$m/[SIII]33.48$\mu$m as a function of [NeIII]15.56$\mu$m/[NeII]12.81$\mu$m which can be useful in identifying the principal excitation mechanism in a galaxy. Galaxies in this diagram split naturally into two branches. Classic AGNs as well as starburst galaxies with an AGN component populate the upper branch, with stronger AGNs displaying higher [NeIII]/[NeII] ratios. BCDs and pure starbursts are located in the lower branch. We find that overall the placement of galaxies on this diagram correlates well with their corresponding locations in the log([NII]/H$\alpha$) vs. log([OIII]/H$\beta$) diagnostic diagram, which has been widely used in the optical. The two diagrams provide consistent classifications of the excitation mechanism in a galaxy. On the other hand, the diagram of [NeIII]15.56$\mu$m/[NeII]12.81$\mu$m vs. [SIV]10.51$\mu$m/[SIII]18.71$\mu$m is not as efficient in separating AGNs from BCDs and pure starbursts. (abridged) Comment: 15 pages, including 1 table and 14 figures. Accepted by ApJ
08/2009;
-
L. Armus,
J. M. Mazzarella,
A. S. Evans,
J. A. Surace,
D. B. Sanders,
K. Iwasawa,
D. T. Frayer,
J. H. Howell,
B. Chan,
A. O. Petric, [......],
J. A. Marshall,
J. E. Melbourne,
J. Rich,
S. Satyapal,
B. Schulz, H. W. W. Spoon,
E. Sturm,
V. U,
S. Veilleux,
K Xu
[show abstract]
[hide abstract]
ABSTRACT: The Great Observatories All-sky LIRG Survey (GOALS) combines data from NASA's Spitzer, Chandra, Hubble and GALEX observatories, together with ground-based data into a comprehensive imaging and spectroscopic survey of over 200 low redshift Luminous Infrared Galaxies (LIRGs). The LIRGs are a complete subset of the IRAS Revised Bright Galaxy Sample (RBGS). The LIRGs targeted in GOALS span the full range of nuclear spectral types defined via traditional optical line-ratio diagrams as well as interaction stages. 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 multi-wavelength GOALS dataset, we present data for the interacting system VV 340 (IRAS F14547+2449). Between 80-95% of the total far-infrared emission (or about 5E11 solar luminosities) originates in VV 340 North. While the IRAC colors of VV 340 North and South are consistent with star-forming galaxies, both the Spitzer IRS and Chandra ACIS data indicate the presence of a buried AGN in VV 340 North. The GALEX far and near-UV fluxes imply a extremely large infrared "excess" (IRX) for the system (IR/FUV = 81) which is well above the correlation seen in starburst galaxies. Most of this excess is driven by VV 340 N, which alone 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 and which hosts a buried AGN, and a face-on starburst (VV 340 South) that dominates the short-wavelength emission. Comment: 17 pages, 2 tables, 7 postscript figures. Accepted for publication in PASP. Updated manuscript includes complete source table (Table 1)
04/2009;
-
L. Armus,
J. Bernard-Salas, H. W. W. Spoon,
J. A. Marshall,
V. Charmandaris,
S. J. U. Higdon,
V. Desai,
L. Hao,
H. I. Teplitz,
D. Devost,
B. R. Brandl,
B. T. Soifer,
and J. R. Houck
[show abstract]
[hide abstract]
ABSTRACT: We present mid-infrared spectra of the nearby ultraluminous infrared galaxy NGC 6240 taken with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. The spectrum of NGC 6240 is dominated by strong fine-structure lines, rotational H2 lines, and polycyclic aromatic hydrocarbon (PAH) emission features. The H2 line fluxes suggest molecular gas at a variety of temperatures. A simple two-temperature fit to the S(0) through S(7) lines implies a mass of ~6.7 × 106 M☉ at T ~ 957 K and ~1.6 × 109 M☉ at T ~ 164 K, or about 15% of the total molecular gas mass in this system. Notably, we have detected the [Ne V] 14.3 μm emission line, with a flux of 5 × 10-14 ergs cm-2 s-1, providing the first direct detection of the buried active galactic nucleus (AGN) in the mid-infrared. Modeling of the total spectral energy distribution (SED) from near- to far-infrared wavelengths requires the presence of a hot dust (T ~ 700 K) component, which we also associate with the buried AGN. The small [Ne V]/[Ne II] and [Ne V]/IR flux ratios, the relative fraction of hot dust emission, and the large 6.2 μm PAH equivalent width (EQW), are all consistent with an apparent AGN contribution of only 3%-5% to the bolometric luminosity. However, correcting the measured [Ne V] flux by the extinction implied by the silicate optical depth and our SED fitting suggests an intrinsic fractional AGN contribution to the bolometric luminosity of ~20%-24% in NGC 6240, which lies within the range implied by fits to the hard X-ray spectrum.
The Astrophysical Journal 12/2008; 640(1):204. · 6.02 Impact Factor
-
L. Armus,
V. Charmandaris, H. W. W. Spoon,
J. R. Houck,
B. T. Soifer,
B. R. Brandl,
P. N. Appleton,
H. I. Teplitz,
S. J. U. Higdon,
D. W. Weedman, [......],
M. J. Burgdorf,
S. B. Fajardo-Acosta,
J. G. Ingalls,
J. Higdon,
L. Hao,
J. Bernard-Salas,
T. Herter,
J. Troeltzsch,
B. Unruh,
and M. Winghart
[show abstract]
[hide abstract]
ABSTRACT: We present spectra taken with the Infrared Spectrograph on the Spitzer Space Telescope covering the 5-38 μm region of three ultraluminous infrared galaxies (ULIRGs): Mrk 1014 (z = 0.163), Mrk 463 (z = 0.051), and UGC 5101 (z = 0.039). The continua of UGC 5101 and Mrk 463 show strong silicate absorption suggesting significant optical depths to the nuclei at 10 μm. UGC 5101 also shows the clear presence of water ice in absorption. Polycyclic aromatic hydrocarbon (PAH) emission features are seen in both Mrk 1014 and UGC 5101, including the 16.4 μm line in UGC 5101. The fine-structure lines are consistent with dominant active galactic nucleus (AGN) power sources in both Mrk 1014 and Mrk 463. In UGC 5101 we detect the [Ne V] 14.3 μm emission line, providing the first direct evidence for a buried AGN in the mid-infrared. The detection of the 9.66 μm and 17.03 μm H2 emission lines in both UGC 5101 and Mrk 463 suggest that the warm molecular gas accounts for 22% and 48% of the total molecular gas masses in these galaxies.
The Astrophysical Journal Supplement Series 12/2008; 154(1):178. · 13.46 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Silicates are an important component of interstellar dust, and the structure of these grains (amorphous or crystalline) is sensitive to the local physical conditions. We have studied the infrared spectra of a sample of ultraluminous infrared galaxies (ULIRGs). Here we report the discovery of weak, narrow absorption features at 11, 16, 19, 23, and 28 μm, characteristic of crystalline silicates, superimposed on the broad absorption bands at 10 and 18 μm due to amorphous silicates in a subset of this sample. These features betray the presence of forsterite (Mg2SiO4), the magnesium-rich end member of the olivines. Previously, crystalline silicates have only been observed in circumstellar environments. The derived fraction of forsterite to amorphous silicates is typically 0.1 in these ULIRGs. This is much larger than the upper limit for this ratio in the interstellar medium of the Milky Way, 0.01. These results suggest that the timescale for injection of crystalline silicates into the ISM is short in a merger-driven starburst environment (e.g., as compared to the total time to dissipate the gas), pointing toward massive stars as a prominent source of crystalline silicates. Furthermore, amorphization due to cosmic rays, which is thought to be of prime importance for the local ISM, lags in vigorous starburst environments.
The Astrophysical Journal 12/2008; 638(2):759. · 6.02 Impact Factor
-
D. Farrah,
J. Bernard-Salas, H. W. W. Spoon,
B. T. Soifer,
L. Armus,
B. Brandl,
V. Charmandaris,
V. Desai,
S. Higdon,
D. Devost,
and J. Houck
[show abstract]
[hide abstract]
ABSTRACT: We present R ~ 600, 10-37 μm spectra of 53 ultraluminous infrared galaxies (ULIRGs), taken using the Infrared Spectrograph on board Spitzer. The spectra show fine-structure emission lines of neon, oxygen, sulfur, silicon, argon, chlorine, iron, and phosphorous; molecular hydrogen lines, and C2H2, HCN, and OH- absorption features. We employ diagnostics based on the fine-structure lines, the polycyclic aromatic hydrocarbon (PAH) features and the 9.7 μm silicate absorption feature, to show that the infrared emission from most ULIRGs is powered mostly by star formation, with only ~20% of ULIRGs hosting an AGN with a greater IR luminosity than the starburst. The detection of [Ne V] λ14.32 in just under half the sample, however, implies that an AGN contributes significantly to the mid-IR flux in ~42% of ULIRGs. The starbursts and AGNs in ULIRGs appear more extincted, and for the starbursts more compact than those in lower luminosity systems. The excitations and electron densities in the narrow-line regions of ULIRGs appear comparable to those of starbursts with L1011.5 L, although the NLR gas in ULIRGs may be more dense. We show that the [Ne II] λ12.81 + [Ne III] λ15.56 luminosity correlates with both infrared luminosity and the luminosity of the 6.2 and 11.2 μm PAH features, and derive a calibration between PAH luminosity and star formation rate. Finally, we show that ULIRGs with silicate absorption strengths Ssil of 0.8 Ssil 2.4 are likely to be powered mainly by star formation, but that ULIRGs with Ssil 0.8, and possibly those with Ssil 2.4, contain an IR-luminous AGN.
The Astrophysical Journal 12/2008; 667(1):149. · 6.02 Impact Factor
-
B. R. Brandl,
J. Bernard-Salas, H. W. W. Spoon,
D. Devost,
G. C. Sloan,
S. Guilles,
Y. Wu,
J. R. Houck,
D. W. Weedman,
L. Armus,
P. N. Appleton,
B. T. Soifer,
V. Charmandaris,
L. Hao,
J. A. Marshall,
S. J. Higdon,
and T. L. Herter
[show abstract]
[hide abstract]
ABSTRACT: We present 5-38 μm mid-infrared spectra at a spectral resolution of R ≈ 65-130 of a large sample of 22 starburst nuclei taken with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. The spectra show a vast range of starburst SEDs. The silicate absorption ranges from essentially no absorption to heavily obscured systems with an optical depth of τ9.8 μm ~ 5. The spectral slopes can be used to discriminate between starburst and AGN powered sources. The monochromatic continuum fluxes at 15 and 30 μm enable a remarkably accurate estimate of the total infrared luminosity of the starburst. We find that the PAH equivalent width is independent of the total starburst luminosity LIR as both continuum and PAH feature scale proportionally. However, the luminosity of the 6.2 μm feature scales with LIR and can be used to approximate the total infrared luminosity of the starburst. Although our starburst sample covers about a factor of 10 difference in the [Ne III]/[Ne II] ratio, we found no systematic correlation between the radiation field hardness and the PAH equivalent width or the 7.7 μm/11.3 μm PAH ratio. These results are based on spatially integrated diagnostics over an entire starburst region, and local variations may be "averaged out." It is presumably due to this effect that unresolved starburst nuclei with significantly different global properties appear spectrally as rather similar members of one class of objects.
The Astrophysical Journal 12/2008; 653(2):1129. · 6.02 Impact Factor
-
A. S. Evans,
T. Vavilkin,
J. Pizagno,
F. Modica,
J. M. Mazzarella,
K. Iwasawa,
J. H. Howell,
J. A. Surace,
L. Armus,
A. O. Petric, H. W. W. Spoon,
J. E. Barnes,
T. A. Suer,
D. B. Sanders,
B. Chan,
and S. Lord
[show abstract]
[hide abstract]
ABSTRACT: New optical Hubble Space Telescope (HST), Spitzer Space Telescope, and XMM observations of the luminous infrared galaxy (LIRG) NGC 2623 are presented. This galaxy was observed as part of the Great Observatories All-sky LIRG Survey (GOALS). The prominent 3.2 kpc southern extension to the nucleus has been resolved by HST observations into ~100 star clusters, making it one of the richest off-nuclear concentrations of bright clusters observed in GOALS. The clusters have to –12.6 mag, which is within the magnitude range of Antennae galaxy clusters and in excess of 30 Doradus clusters at the high end. Their optical colors are primarily consistent with ages of ~1-100 Myr. Archival GALEX data show the off-nuclear region to be extremely bright in the far-ultraviolet, being equivalent in luminosity to the resolved nuclear region at 0.15 μm, but becoming less energetically significant at increasing wavelengths. In addition, [Ne V] 14.3 μm emission is detected with Spitzer IRS, confirming the inference from the X-ray and radio data that an active galactic nucleus (AGN) is present. Thus, the off-nuclear optical clusters are associated with a secondary burst of activity corresponding to a star formation rate ~0.1-0.2 M☉ yr−1; the bulk of infrared (and thus bolometric) luminosity is generated via star formation and an AGN embedded behind dust within the inner kiloparsec of the system. If the infrared luminosity is primarily reprocessed starlight, the off-nuclear starburst accounts for <1% of the present star formation in NGC 2623.
The Astrophysical Journal 12/2008; 675(2):L69. · 6.02 Impact Factor
-
Lei Hao, H. W. W. Spoon,
G. C. Sloan,
J. A. Marshall,
L. Armus,
A. G. G. M. Tielens,
B. Sargent,
I. M. van Bemmel,
V. Charmandaris,
D. W. Weedman,
and J. R. Houck
[show abstract]
[hide abstract]
ABSTRACT: We report the spectroscopic detection of silicate emission at 10 and 18 μm in five PG quasars, the first detection of these two features in galaxies outside the Local Group. This finding is consistent with the unification model for active galactic nuclei (AGNs), which predicts that an AGN torus seen pole-on should show a silicate emission feature in the mid-infrared. The strengths of the detected silicate emission features range from 0.12 to 1.25 times the continuum at 10 μm and from 0.20 to 0.79 times the continuum at 18 μm. The silicate grain temperatures inferred from the ratio of 18 μm to 10 μm silicate features under the assumption of optically thin emission range from 140 to 220 K.
The Astrophysical Journal 12/2008; 625(2):L75. · 6.02 Impact Factor
