424 research outputs found
CO line emission in the halo of a radio galaxy at z=2.6
We report the detection of luminous CO(3-2) line emission in the halo of the
z=2.6 radio galaxy (HzRG) TXS0828+193, which has no detected counterpart at
optical to mid-infrared wavelengths implying a stellar mass < few x10^9 M_sun
and relatively low star-formation rates. With the IRAM PdBI we find two CO
emission line components at the same position at ~80 kpc distance from the HzRG
along the axis of the radio jet, with different blueshifts of few 100 km s^-1
relative to the HzRG and a total luminosity of ~2x10^10 K km s^-1 pc^2 detected
at 8 sigma significance. HzRGs have significant galaxy overdensities and
extended halos of metal-enriched gas often with embedded clouds or filaments of
denser material, and likely trace very massive dark-matter halos. The CO
emission may be associated with a gas-rich, low-mass satellite galaxy with
little on-going star formation, in contrast to all previous CO detections of
galaxies at similar redshifts. Alternatively, the CO may be related to a gas
cloud or filament and perhaps jet-induced gas cooling in the outer halo,
somewhat in analogy with extended CO emission found in low-redshift galaxy
clusters.Comment: MNRAS Letters, accepte
NICMOS Imaging of Infrared-Luminous Galaxies
We present near-infrared images obtained with the HST NICMOS camera for a
sample of 9 luminous (LIGs: L_IR (8-1000 microns) >~ 10^11 L_sun) and 15
ultra-luminous (ULIGS: L_IR >~ 10^12 L_sun) infrared galaxies. The sample
includes representative systems classified as warm (f_25/f_60 > 0.2) and cold
(f_25/f_60 <~ 0.2) based on the mid-infrared colors and systems with nuclear
emission lines classified as HII (i.e. starburst), QSO, Seyfert and LINER. The
morphologies of the sample galaxies are diverse and provide further support for
the idea that they are created by the collision or interactions of spiral
galaxies. Although no new nuclei are seen in the NICMOS images, the NICMOS
images do reveal new spiral structures, bridges, and circumnuclear star
clusters...Comment: LaTex, 27 pages with 14 gif and 4 jpg figures, AJ, in press, contour
figures of the NICMOS images can be viewed at
http://nedwww.ipac.caltech.edu/level5/Scoville/frames.htm
What Powers Ultra-luminous IRAS Galaxies?
We present an ISO SWS and ISOPHOT-S, mid-infrared spectroscopic survey of 15
ultra-luminous IRAS galaxies. We combine the survey results with a detailed
case study, based on near-IR and mm imaging spectroscopy, of one of the sample
galaxies (UGC 5101). We compare the near- and mid-IR characteristics of these
ultra-luminous galaxies to ISO and literature data of thirty starburst and
active galactic nuclei (AGN), template galaxies. We find that
1) 70-80% of the ultra-luminous IRAS galaxies in our sample are predominantly
powered by recently formed massive stars. 20-30% are powered by a central AGN.
These conclusions are based on a new infrared 'diagnostic diagram' involving
the ratio of high to low excitation mid-IR emission lines on the one hand, and
on the strength of the 7.7um PAH feature on the other hand.
2) at least half of the sources probably have simultaneously an active
nucleus and starburst activity in a 1-2 kpc diameter circum-nuclear disk/ring.
3) the mid-infrared emitting regions are highly obscured. After correction
for these extinctions, we estimate that the star forming regions in ULIRGs have
ages between 10^7 and 10^8 years, similar to but somewhat larger than those
found in lower luminosity starburst galaxies.
4) in the sample we have studied there is no obvious trend for the AGN
component to dominate in the most compact, and thus most advanced mergers.
Instead, at any given time during the merger evolution, the time dependent
compression of the circum-nuclear interstellar gas, the accretion rate onto the
central black hole and the associated radiation efficiency may determine
whether star formation or AGN activity dominates the luminosity of the system.Comment: 63 pages postscript (ex. MS Word), 11 postscript and 2 gif figures,
submitted to ApJ. See also
http://www.mpe-garching.mpg.de/ISO/preprint/MPE-IR-97003.htm
Far-Infrared Line Deficits in Galaxies with Extreme Lfir/MH2 Ratios
We report initial results from the far-infrared fine structure line
observations of a sample of 44 local starbursts, Seyfert galaxies and infrared
luminous galaxies obtained with the PACS spectrometer on board Herschel. We
show that the ratio between the far-infrared luminosity and the molecular gas
mass, Lfir/MH2, is a much better proxy for the relative brightness of the
far-infrared lines than Lfir alone. Galaxies with high Lfir/MH2 ratios tend to
have weaker fine structure lines relative to their far-infrared continuum than
galaxies with Lfir/MH2 < 80 Lsun/Msun. A deficit of the [C II] 158 micron line
relative to Lfir was previously found with the ISO satellite, but now we show
for the first time that this is a general aspect of all far-infrared fine
structure lines, regardless of their origin in the ionized or neutral phase of
the interstellar medium. The Lfir/MH2 value where these line deficits start to
manifest is similar to the limit that separates between the two modes of star
formation recently found in galaxies on the basis of studies of their gas-star
formation relations. Our finding that the properties of the interstellar medium
are also significantly different in these regimes provides independent support
for the different star forming relations in normal disk galaxies and major
merger systems. We use the spectral synthesis code Cloudy to model the emission
of the lines. The expected increase of the ionization parameter with Lfir/MH2
can simultaneously explain the line deficits in the [C II], [N II] and [O I]
lines.Comment: Accepted for publication in ApJ Letters; 5 pages, 3 figure
Disk, merger, or outflow ? Molecular gas kinematics in two powerful obscured QSOs at z>3.4
We report on the detection of bright CO(4-3) line emission in two powerful,
obscured quasars discovered in the SWIRE survey, SW022513 and SW022550 at
z>3.4. We analyze the line strength and profile to determine the gas mass,
dynamical mass and the gas dynamics for both galaxies. In SW022513 we may have
found the first evidence for a molecular, AGN-driven wind in the early
Universe. The line profile in SW022513 is broad (FWHM = 1000 km/s) and
blueshifted by -200 km/s relative to systemic (where the systemic velocity is
estimated from the narrow components of ionized gas lines, as is commonly done
for AGN at low and high redshifts). SW022550 has a more regular, double-peaked
profile, which is marginally spatially resolved in our data, consistent with
either a merger or an extended disk. The molecular gas masses, 4x10^10 Msun,
are large and account for <30% of the stellar mass, making these obscured QSOs
as gas rich as other powerful CO emitting galaxies at high redshift, i.e.,
submillimeter galaxies. Our sources exhibit relatively lower star-formation
efficiencies compared to other dusty, powerful starburst galaxies at high
redshift. We speculate that this could be a consequence of the AGN perturbing
the molecular gas.Comment: Accepted for publication in A&
Extragalactic millimeter-wave sources in South Pole Telescope survey data: source counts, catalog, and statistics for an 87 square-degree field
We report the results of an 87 square-degree point-source survey centered at
R.A. 5h30m, decl. -55 deg. taken with the South Pole Telescope (SPT) at 1.4 and
2.0 mm wavelengths with arc-minute resolution and milli-Jansky depth. Based on
the ratio of flux in the two bands, we separate the detected sources into two
populations, one consistent with synchrotron emission from active galactic
nuclei (AGN) and one consistent with thermal emission from dust. We present
source counts for each population from 11 to 640 mJy at 1.4 mm and from 4.4 to
800 mJy at 2.0 mm. The 2.0 mm counts are dominated by synchrotron-dominated
sources across our reported flux range; the 1.4 mm counts are dominated by
synchroton-dominated sources above ~15 mJy and by dust-dominated sources below
that flux level. We detect 141 synchrotron-dominated sources and 47
dust-dominated sources at S/N > 4.5 in at least one band. All of the most
significantly detected members of the synchrotron-dominated population are
associated with sources in previously published radio catalogs. Some of the
dust-dominated sources are associated with nearby (z << 1) galaxies whose dust
emission is also detected by the Infrared Astronomy Satellite (IRAS). However,
most of the bright, dust-dominated sources have no counterparts in any existing
catalogs. We argue that these sources represent the rarest and brightest
members of the population commonly referred to as sub-millimeter galaxies
(SMGs). Because these sources are selected at longer wavelengths than in
typical SMG surveys, they are expected to have a higher mean redshift
distribution and may provide a new window on galaxy formation in the early
universe.Comment: 35 emulateapj pages, 12 figures, 5 table
Far-Infrared Properties of Spitzer-selected Luminous Starbursts
We present SHARC-2 350 micron data on 20 luminous z ~ 2 starbursts with
S(1.2mm) > 2 mJy from the Spitzer-selected samples of Lonsdale et al. and
Fiolet et al. All the sources were detected, with S(350um) > 25 mJy for 18 of
them. With the data, we determine precise dust temperatures and luminosities
for these galaxies using both single-temperature fits and models with power-law
mass--temperature distributions. We derive appropriate formulae to use when
optical depths are non-negligible. Our models provide an excellent fit to the
6um--2mm measurements of local starbursts. We find characteristic
single-component temperatures T1 ~ 35.5+-2.2 K and integrated infrared (IR)
luminosities around 10^(12.9+-0.1) Lsun for the SWIRE-selected sources.
Molecular gas masses are estimated at 4 x 10^(10) Msun, assuming
kappa(850um)=0.15 m^2/kg and a submillimeter-selected galaxy (SMG)-like
gas-to-dust mass ratio. The best-fit models imply >~2 kpc emission scales. We
also note a tight correlation between rest-frame 1.4 GHz radio and IR
luminosities confirming star formation as the predominant power source. The
far-IR properties of our sample are indistinguishable from the purely
submillimeter-selected populations from current surveys. We therefore conclude
that our original selection criteria, based on mid-IR colors and 24 um flux
densities, provides an effective means for the study of SMGs at z ~ 1.5--2.5.Comment: 13 pages, 4 figures, edited to match published version in ApJ 717,
29-39 (2010
Molecular Hydrogen Excitation around Active Galactic Nuclei
We report R~3000 VLT ISAAC K-band spectroscopy of the nuclei (i.e. central
100-300pc) of 9 galaxies hosting an active galactic nucleus. For 5 of these we
also present spectra of the circumnuclear region out to 1kpc. We have measured
a number of H_2 lines in the v=1-0, 2-1, and 3-2 vibrational transitions, as
well as the Br_gamma and HeI recombination lines, and the NaI stellar
absorption. Although only 3 of the galaxies are classified as Seyfert 1s in the
literature, broad Br_gamma (FWHM 1000kms) is seen in 7 of the objects. The
v=1-0 emission appears thermalised at T~1000K. However, the v=2-1 and 3-2
emission show evidence of being radiatively excited by far-UV photons. The PDR
models that fit the data best are, as for the ultraluminous infrared galaxies
in Davies et al. (2003), those for which the H_2 emission arises in dense
clouds illuminated by intense FUV radiation. The NaI stellar absorption is
clearly seen in 6 of the nuclear spectra, indicating the presence of a
significant population of late type stars. It is possible that these stars are
a result of the same episode of star formation that gave rise to the stars
heating the PDRs. It seems unlikely that the AGN is the dominant source of
excitation for the near infrared H_2 emission: in two nuclei H_2 was not
detected at all, and in general we find no evidence of suppression of the
2-1S(3) line, which may occur in X-ray irradiated gas. Our data do not reveal
any significant difference between the nuclear and circumnuclear line ratios,
suggesting that the physical conditions of the dominant excitation mechanism
are similar both near the AGN and in the larger scale environment around it,
and that star formation is an important process even in the central 100pc
acround AGN.Comment: accepted for publication in ApJ (32 pages, 12 figures
The evolution of the dust and gas content in galaxies
We use deep Herschel observations taken with both PACS and SPIRE imaging cameras to estimate the dust mass of a sample of galaxies extracted from the GOODS-S, GOODS-N and the COSMOS fields. We divide the redshiftâstellar mass (M star )âstar formation rate (SFR) parameter space into small bins and investigate average properties over this grid. In the first part of the work we investigate the scaling relations between dust mass, stellar mass and SFR out to z = 2.5. No clear evolution of the dust mass with redshift is observed at a given SFR and stellar mass. We find a tight correlation between the SFR and the dust mass, which, under reasonable assumptions, is likely a consequence of the Schmidt-Kennicutt (S-K) relation. The previously observed correlation between the stellar content and the dust content flattens or sometimes disappears when considering galaxies with the same SFR. Our finding suggests that most of the correlation between dust mass and stellar mass obtained by previous studies is likely a consequence of the correlation between the dust mass and the SFR combined with the main sequence, i.e., the tight relation observed between the stellar mass and the SFR and followed by the majority of star-forming galaxies. We then investigate the gas content as inferred from dust mass measurements. We convert the dust mass into gas mass by assuming that the dust-to-gas ratio scales linearly with the gas metallicity (as supported by many observations). For normal star-forming galaxies (on the main sequence) the inferred relation between the SFR and the gas mass (integrated S-K relation) broadly agrees with the results of previous studies based on CO measurements, despite the completely different approaches. We observe that all galaxies in the sample follow, within uncertainties, the same S-K relation. However, when investigated in redshift intervals, the S-K relation shows a moderate, but significant redshift evolution. The bulk of the galaxy population at z ⌠2 converts gas into stars with an efficiency (star formation efficiency, SFE = SFR/M gas , equal to the inverse of the depletion time) about 5 times higher than at z ⌠0. However, it is not clear what fraction of such variation of the SFE is due to an intrinsic redshift evolution and what fraction is simply a consequence of high-z galaxies having, on average, higher SFR, combined with thesuper-linear slope of the S-K relation (whileother studies finda linear slope). We confirm that the gas fraction (f gas = M gas /(M gas + M star )) decreases with stellar mass and increases with the SFR. We observe no evolution with redshift once M star and SFR are fixed. We explain these trends by introducing a universal relation between gas fraction, stellar mass and SFR that does not evolve with redshift, at least out to z ⌠2.5. Galaxies move across this relation as their gas content evolves across the cosmic epochs. We use the 3D fundamental f gas âM star âSFR relation, along with the evolution of the main sequence with redshift, to estimate the evolution of the gas fraction in the average population of galaxies as a function of redshift and as a function of stellar mass: we find that M star > ⌠10 11 M ? galaxies show the strongest evolution at z > ⌠1.3 and a flatter trend at lower redshift, while f gas decreases more regularly over the entire redshift range probed in M star < ⌠10 11 Mo galaxies, in agreement with a downsizing scenario
Physical properties of Lyman-alpha emitters at from UV-to-FIR measurements
The analysis of the physical properties of low-redshift Ly emitters
(LAEs) can provide clues in the study of their high-redshift analogues. At , LAEs are bright enough to be detected over almost the entire
electromagnetic spectrum and it is possible to carry out a more precise and
complete study than at higher redshifts. In this study, we examine the UV and
IR emission, dust attenuation, SFR and morphology of a sample of 23
GALEX-discovered star-forming (SF) LAEs at with direct UV (GALEX),
optical (ACS) and FIR (PACS and MIPS) data. Using the same UV and IR limiting
luminosities, we find that LAEs at tend to be less dusty, have
slightly higher total SFRs, have bluer UV continuum slopes, and are much
smaller than other galaxies that do not exhibit Ly emission in their
spectrum (non-LAEs). These results suggest that at Ly
photons tend to escape from small galaxies with low dust attenuation. Regarding
their morphology, LAEs belong to Irr/merger classes, unlike non-LAEs. Size and
morphology represent the most noticeable difference between LAEs and non-LAEs
at . Furthermore, the comparison of our results with those obtained
at higher redshifts indicates that either the Ly technique picks up
different kind of galaxies at different redshifts or that the physical
properties of LAEs are evolving with redshift.Comment: Accepted for publication in Ap
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