386 research outputs found
The Infrared Database of Extragalactic Observables from Spitzer I: the redshift catalog
This is the first of a series of papers on the Infrared Database of
Extragalactic Observables from Spitzer (IDEOS). In this work we describe the
identification of optical counterparts of the infrared sources detected in
Spitzer Infrared Spectrograph (IRS) observations, and the acquisition and
validation of redshifts. The IDEOS sample includes all the spectra from the
Cornell Atlas of Spitzer/IRS Sources (CASSIS) of galaxies beyond the Local
Group. Optical counterparts were identified from correlation of the extraction
coordinates with the NASA Extragalactic Database (NED). To confirm the optical
association and validate NED redshifts, we measure redshifts with unprecedented
accuracy on the IRS spectra ({\sigma}(dz/(1+z))=0.0011) by using an improved
version of the maximum combined pseudo-likelihood method (MCPL). We perform a
multi-stage verification of redshifts that considers alternate NED redshifts,
the MCPL redshift, and visual inspection of the IRS spectrum. The statistics is
as follows: the IDEOS sample contains 3361 galaxies at redshift 0<z<6.42 (mean:
0.48, median: 0.14). We confirm the default NED redshift for 2429 sources and
identify 124 with incorrect NED redshifts. We obtain IRS-based redshifts for
568 IDEOS sources without optical spectroscopic redshifts, including 228 with
no previous redshift measurements. We provide the entire IDEOS redshift catalog
in machine-readable formats. The catalog condenses our compilation and
verification effort, and includes our final evaluation on the most likely
redshift for each source, its origin, and reliability estimates.Comment: 11 pages, 6 figures, 1 table. Accepted for publication in MNRAS. Full
redshift table in machine-readable format available at
http://ideos.astro.cornell.edu/redshifts.htm
Vibrationally excited HC3N in NGC 4418
We investigate the molecular gas properties of the deeply obscured luminous
infrared galaxy NGC 4418. We address the excitation of the complex molecule
HC3N to determine whether its unusually luminous emission is related to the
nature of the buried nuclear source. We use IRAM 30m and JCMT observations of
rotational and vibrational lines of HC3N to model the excitation of the
molecule by means of rotational diagrams. We report the first confirmed
extragalactic detection of vibrational lines of HC3N. We detect 6 different
rotational transitions ranging from J=10-9 to J=30-29 in the ground vibrational
state and obtain a tentative detection of the J=38-37 line. We also detect 7
rotational transitions of the vibrationally excited states v6 and v7, with
angular momenta ranging from J=10-9 to 28-27. The energies of the upper states
of the observed transitions range from 20 to 850 K. In the optically thin
regime, we find that the rotational transitions of the vibrational ground state
can be fitted for two temperatures, 30 K and 260 K, while the vibrationally
excited levels can be fitted for a rotational temperature of 90 K and a
vibrational temperature of 500 K. In the inner 300 pc of NGC 4418, we estimate
a high HC3N abundance, of the order of 10^-7. The excitation of the HC3N
molecule responds strongly to the intense radiation field and the presence of
warm, dense gas and dust at the center of NGC 4418. The intense HC3N line
emission is a result of both high abundances and excitation. The properties of
the HC3N emitting gas are similar to those found for hot cores in Sgr B2, which
implies that the nucleus (< 300 pc) of NGC 4418 is reminiscent of a hot core.
The potential presence of a compact, hot component (T=500 K) is also discussed
CO-Dark Star Formation and Black Hole Activity in 3C 368 at z = 1.131: Coeval Growth of Stellar and Supermassive Black Hole Masses
We present the detection of four far-infrared fine-structure oxygen lines, as
well as strong upper limits for the CO(2-1) and [N II] 205 um lines, in 3C 368,
a well-studied radio-loud galaxy at z = 1.131. These new oxygen lines, taken in
conjunction with previously observed neon and carbon fine-structure lines,
suggest a powerful active galactic nucleus (AGN), accompanied by vigorous and
extended star formation. A starburst dominated by O8 stars, with an age of ~6.5
Myr, provides a good fit to the fine-structure line data. This estimated age of
the starburst makes it nearly concurrent with the latest episode of AGN
activity, suggesting a link between the growth of the supermassive black hole
and stellar population in this source. We do not detect the CO(2-1) line, down
to a level twelve times lower than the expected value for star forming
galaxies. This lack of CO line emission is consistent with recent star
formation activity if the star-forming molecular gas has low metallicity, is
highly fractionated (such that CO is photodissociated through much of the
clouds), or is chemically very young (such that CO has not yet had time to
form). It is also possible, though we argue unlikely, that the ensemble of fine
structure lines are emitted from the region heated by the AGN.Comment: 10 pages, 4 figures, 2 tables, accepted for publication in the
Astrophysical Journa
Extended Warm Gas in the ULIRG Mrk273: Galactic Outflows and Tidal Debris
We present new HST ACS medium- and narrow-band images and long-slit, optical
(4000 - 7200A) spectra obtained using the Isaac Newton Telescope (INT) on La
Palma, of the merging system Mrk273. The HST observations sample the
[OIII]4959,5007 emission from the galaxy and the nearby continuum. The images
show that the morphologies of the extended continuum and the ionised gas
emission from the galaxy are decoupled, extending almost perpendicular to each
other. In particular, we detect for the first time a spectacular structure of
ionised gas in the form of filaments extending ~23 kpc to the east of the
nuclear region. The quiescent ionised gas kinematics at these locations
suggests that these filaments are tidal debris left over from a secondary
merger event that are illuminated by an AGN in the nuclear regions. The images
also reveal a complex morphology in the nuclear region of the galaxy for both
the continuum and the [OIII] emission. Kinematic disturbance, in the form of
broad (FWHM > 500 km s-1) and/or strongly shifted (abs(\DeltaV) >150 km s-1)
emission line components, is found at almost all locations within a radius of
~4 kpc to the east and west of the northern nucleus. We fit the profiles of all
the emission lines of different ionisation with a kinematic model using up to 3
Gaussian components. From these fits we derive diagnostic line ratios that are
used to investigate the ionisation mechanisms at the different locations in the
galaxy. We show that, in general, the line ratios are consistent with
photoionization by an AGN as the main ionisation mechanism. Finally, the
highest surface brightness [OIII] emission is found in a compact region that is
coincident with the so-called SE nuclear component. The compactness, kinematics
and emission line ratios of this component suggest that it is a separate
nucleus with its own AGN.Comment: Accepted for Publication in A&
The Complex Structure of the Multi-Phase Galactic Wind in a Starburst Merger
Neutral outflows have been detected in many ultraluminous infrared galaxies
(ULIRGs) via the Na I D absorption-line doublet.
For the first time, we have mapped and analyzed the 2-D kinematics of a cool
neutral outflow in a ULIRG, F10565+2448, using the integral field unit (IFU) on
Gemini North to observe the Na I D feature. At the same time we have mapped the
ionized outflow with the [NII] and H emission lines. We find a systemic
rotation curve that is consistent with the rotation of the molecular disk
determined from previous CO observations. The absorption lines show evidence of
a nuclear outflow with a radial extent of at least 3 kpc, consistent with
previous observations. The strength of the Na I D lines have a strong,
spatially resolved correlation with reddening, suggesting that dust is present
in the outflow. Surprisingly, the outflow velocities of the neutral gas show a
strong asymmetry in the form of a major-axis gradient that is opposite in sign
to disk rotation. This is inconsistent with entrained material rotating along
with the galaxy or with a tilted minor-axis outflow. We hypothesize that this
unusual behavior is due to an asymmetry in the distribution of the ambient gas.
We also see evidence of asymmetric ionized outflow in the emission-line
velocity map, which appear to be decoupled from the neutral outflow. Our
results strengthen the hypothesis that ULIRG outflows differ in morphology from
those in more quiescent disk galaxies.Comment: Accepted to Ap
The Mid-IR Properties of Starburst Galaxies from Spitzer-IRS Spectroscopy
We present 5-38um 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 in
starburst SEDs. The silicate absorption ranges from essentially no absorption
to heavily obscured systems with an optical depth of tau(9.8um)~5. The spectral
slopes can be used to discriminate between starburst and AGN powered sources.
The monochromatic continuum fluxes at 15um and 30um 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
L_IR as both continuum and PAH feature scale proportionally. However, the
luminosity of the 6.2um feature scales with L_IR and can be used to approximate
the total infrared luminosity of the starburst. Although our starburst sample
covers about a factor of ten difference in the [NeIII]/[NeII] ratio, we found
no systematic correlation between the radiation field hardness and the PAH
equivalent width or the 7.7um/11.3um 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.Comment: 22 pages, accepted for publication in ApJ, a high-resolution version
is available from http://www.strw.leidenuniv.nl/~brandl/IRS_starbursts.pd
Deep Mid-Infrared Silicate Absorption as a Diagnostic of Obscuring Geometry Toward Galactic Nuclei
The silicate cross section peak near 10um produces emission and absorption
features in the spectra of dusty galactic nuclei observed with the Spitzer
Space Telescope. Especially in ultraluminous infrared galaxies, the observed
absorption feature can be extremely deep, as IRAS 08572+3915 illustrates. A
foreground screen of obscuration cannot reproduce this observed feature, even
at large optical depth. Instead, the deep absorption requires a nuclear source
to be deeply embedded in a smooth distribution of material that is both
geometrically and optically thick. In contrast, a clumpy medium can produce
only shallow absorption or emission, which are characteristic of
optically-identified active galactic nuclei. In general, the geometry of the
dusty region and the total optical depth, rather than the grain composition or
heating spectrum, determine the silicate feature's observable properties. The
apparent optical depth calculated from the ratio of line to continuum emission
generally fails to accurately measure the true optical depth. The obscuring
geometry, not the nature of the embedded source, also determines the far-IR
spectral shape.Comment: To appear in ApJ
Spitzer mid-infrared spectroscopy of compact symmetric objects: What powers radio-loud active galactic nuclei?
We present low- and high-resolution mid-infrared (mid-IR) spectra and
photometry for eight compact symmetric objects (CSOs) taken with the Infrared
Spectrograph on the Spitzer Space Telescope. The hosts of these young, powerful
radio galaxies show significant diversity in their mid-IR spectra. This
includes multiple atomic fine-structure lines, H2 gas, polycyclic aromatic
hydrocarbon (PAH) emission, warm dust from T = 50 to 150 K, and silicate
features in both emission and absorption. There is no evidence in the mid-IR of
a single template for CSO hosts, but 5/8 galaxies show similar moderate levels
of star formation (<10 M_sun/yr from PAH emission) and silicate dust in a
clumpy torus. The total amount of extinction ranges from A_V ~ 10 to 30, and
the high-ionization [Ne V] 14.3 and 24.3 um transitions are not detected for
any galaxy in the sample. Almost all CSOs show contributions both from star
formation and active galactic nuclei (AGNs), suggesting that they occupy a
continuum between pure starbursts and AGNs. This is consistent with the
hypothesis that radio galaxies are created following a galactic merger; the
timing of the radio activity onset means that contributions to the IR
luminosity from both merger-induced star formation and the central AGN are
likely. Bondi accretion is capable of powering the radio jets for almost all
CSOs in the sample; the lack of [Ne V] emission suggests an advection-dominated
accretion flow mode as a possible candidate. Merging black holes (BHs) with
M_BH > 10^8 M_sun likely exist in all of the CSOs in the sample; however, there
is no direct evidence from these data that BH spin energy is being tapped as an
alternative mode for powering the radio jets.Comment: 22 pages, 14 figures; published in Ap
High resolution mid-infrared spectroscopy of ultraluminous infrared galaxies
(Abridged) We present R~600, 10-37um spectra of 53 ULIRGs at z<0.32, taken
using the IRS on board Spitzer. All of the spectra show fine structure emission
lines of Ne, O, S, Si and Ar, as well as molecular Hydrogen lines. Some ULIRGs
also show emission lines of Cl, Fe, P, and atomic Hydrogen, and/or absorption
features from C_2H_2, HCN, and OH. We employ diagnostics based on the
fine-structure lines, as well as the EWs and luminosities of PAH features and
the strength of the 9.7um silicate absorption feature (S_sil), to explore the
power source behind the infrared emission in ULIRGs. We show that the IR
emission from the majority of ULIRGs is powered mostly by star formation, with
only ~20% of ULIRGs hosting an AGN with a comparable or greater IR luminosity
than the starburst. The detection of the 14.32um [NeV] line in just under half
the sample however implies that an AGN contributes significantly to the mid-IR
flux in ~42% of ULIRGs. The emission line ratios, luminosities and PAH EWs are
consistent with the starbursts and AGN in ULIRGs being more extincted, and for
the starbursts more compact, versions of those in lower luminosity systems. The
excitations and electron densities in the NLRs of ULIRGs appear comparable to
those of lower luminosity starbursts, though there is evidence that the NLR gas
in ULIRGs is more dense. We show that the combined luminosity of the 12.81um
[NeII] and 15.56um [NeIII] lines correlates with both IR luminosity and the
luminosity of the 6.2 micron and 11.2 micron PAH features in ULIRGs, and use
this to derive a calibration between PAH luminosity and star formation rate.
Finally, we show that ULIRGs with 0.8 < S_sil < 2.4 are likely to be powered
mainly by star formation, but that ULIRGs with S_sil < 0.8, and possibly those
with S_sil > 2.4, contain an IR-luminous AGN.Comment: 62 pages in preprint format, 4 tables, 23 figures. ApJ accepte
Water in Comet 2/2003 K4 (LINEAR) with Spitzer
We present sensitive 5.5 to 7.6 micron spectra of comet C/2003 K4 (LINEAR)
obtained on 16 July 2004 (r_{h} = 1.760 AU, Delta_{Spitzer} = 1.409 AU, phase
angle 35.4 degrees) with the Spitzer Space Telescope. The nu_{2} vibrational
band of water is detected with a high signal-to-noise ratio (> 50). Model
fitting to the best spectrum yields a water ortho-to-para ratio of 2.47 +/-
0.27, which corresponds to a spin temperature of 28.5^{+6.5}_{-3.5} K. Spectra
acquired at different offset positions show that the rotational temperature
decreases with increasing distance from the nucleus, which is consistent with
evolution from thermal to fluorescence equilibrium. The inferred water
production rate is (2.43 +/- 0.25) \times 10^{29} molec. s^{-1}. The spectra do
not show any evidence for emission from PAHs and carbonate minerals, in
contrast to results reported for comets 9P/Tempel 1 and C/1995 O1 (Hale-Bopp).
However, residual emission is observed near 7.3 micron the origin of which
remains unidentified.Comment: 33 pages, including 11 figures, 2 tables, ApJ 2007 accepte
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