93 research outputs found
Star formation and the interstellar medium in z>6 UV-luminous Lyman-break galaxies
We present Atacama Large Millimeter Array (ALMA) detections of atomic carbon
line and dust continuum emission in two UV-luminous galaxies at redshift 6. The
far-infrared (FIR) luminosities of these galaxies are substantially lower than
similar starbursts at later cosmic epochs, indicating an evolution in the dust
properties with redshift, in agreement with the evolution seen in ultraviolet
(UV) attenuation by dust. The [CII] to FIR ratios are found to be higher than
at low redshift showing that [CII] should be readily detectable by ALMA within
the reionization epoch. One of the two galaxies shows a complex merger nature
with the less massive component dominating the UV emission and the more massive
component dominating the FIR line and continuum. Using the interstellar atomic
carbon line to derive the systemic redshifts we investigate the velocity of
Lyman alpha emission emerging from high-z galaxies. In contrast to previous
work, we find no evidence for decreasing Lyman alpha velocity shifts at
high-redshift. We observe an increase in velocity shifts from z2 to
z6, consistent with the effects of increased IGM absorption.Comment: 10 pages, 9 figures, submitted to ApJ, revised after referees
comment
Constraints on the presence of water megamaser emission in z~2.5 ultraluminous infrared starburst galaxies
We present Expanded Very Large Array and Arecibo observations of two lensed
submm galaxies at z~2.5, in order to search for redshifted 22.235 GHz water
megamaser emission. Both SMM J14011+0252 and SMM J16359+6612 have
multi-wavelength characteristics consistent with ongoing starburst activity, as
well as CO line emission indicating the presence of warm molecular gas. Our
observations do not reveal any evidence for H2O megamaser emission in either
target, while the lensing allows us to obtain deep limits to the H_2O line
luminosities, L(H2O) < 7470 Lsun (3-sigma) in the case of SMM J14011+0252, and
L(H2O) < 1893 Lsun for SMM J16359+6612, assuming linewidths of 80 km/s. Our
search for, and subsequent non-detection of H2O megamaser emission in two
strongly lensed starburst galaxies, rich in gas and dust, suggests that such
megamaser emission is not likely to be common within the unlensed population of
high-redshift starburst galaxies. We use the recent detection of strong H2O
megamaser emission in the lensed quasar, MG J0414+0534 at z = 2.64 to make
predictions for future EVLA C-band surveys of H2O megamaser emission in submm
galaxies hosting AGN.Comment: AJ accepte
Dense Molecular Gas Excitation in Nuclear Starbursts at High Redshift: HCN, HNC, and HCO+(J=6-5) Emission in the z=3.91 Quasar Host of APM08279+5255
We report the detection of surprisingly strong HCN, HNC, and HCO+(J=6-5)
emission in the host galaxy of the z=3.91 quasar APM08279+5255 through
observations with CARMA. HCN, HNC, and HCO+ are typically used as star
formation indicators, tracing dense molecular hydrogen gas [n(H2) > 10^5,cm^-3]
within star-forming molecular clouds. However, the strength of their respective
line emission in the J=6-5 transitions in APM08279+5255 is extremely high,
suggesting that they are excited by another mechanism besides collisions in the
dense molecular gas phase alone. We derive J=6-5 line luminosities of
L'(HCN)=(4.9+/-0.6), L'(HNC)=(2.4+/-0.7), and L'(HCO+)=(3.0+/-0.6)x10^10
(mu_L)^-1 K km/s pc^2 (where mu_L is the lensing magnification factor),
corresponding to L' ratios of ~0.23-0.46 relative to CO(J=1-0). Such high line
ratios would be unusual even in the respective ground-state (J=1-0)
transitions, and indicate exceptional, collisionally and radiatively driven
excitation conditions in the dense, star-forming molecular gas in
APM08279+5255. Through an expansion of our previous modeling of the HCN line
excitation in this source, we show that the high rotational line fluxes are
caused by substantial infrared pumping at moderate opacities in a ~220K warm
gas and dust component. This implies that standard M_dense/L' conversion
factors would substantially overpredict the dense molecular gas mass M_dense.
We also find a HCN J=6-5/5-4 L' ratio greater than 1 (1.36+/-0.31) - however,
our models show that the excitation is likely not `super-thermal', but that the
high line ratio is due to a rising optical depth between both transitions.
These findings are consistent with the picture that the bulk of the gas and
dust in this source is situated in a compact, nuclear starburst, where both the
highly active galactic nucleus and star formation contribute to the heating.Comment: 8 pages, 5 figures, to appear in ApJ (accepted October 8, 2010
A Search for C II 158 μm Line Emission in HCM 6A, a Lyα Emitter at z = 6.56
We report a Plateau de Bure Interferometer search for CII 158μm emission from HCM 6A, a lensed Lyα emitter
(LAE) at z = 6.56. Our non-detections of CII 158μm line emission and 1.2 mm radio continuum emission yield
3σ limits of L_CII < 6.4×10^7×(ΔV/100 km s^−1)^(1/2) L_☉ for the CII 158μm line luminosity and S1.2mm < 0.68 mJy
for the 1.2 mm flux density. The local conversion factor between L_CII and the star formation rate (SFR) yields
an SFR<4.7M_☉ yr^−1, ≈2 times lower than that inferred from the ultraviolet (UV) continuum, suggesting that
the local factor may not be applicable in high-z LAEs. The non-detection of 1.2 mm continuum emission yields a
total SFR<28M_☉ yr^−1; any obscured star formation is thus within a factor of two of the visible star formation.
Our best-fit model to the rest-frame UV/optical spectral energy distribution of HCM 6A yields a stellar mass
of 1.3 × 10^9 M_☉ and an SFR of ≈10M_☉ yr^−1, with negligible dust obscuration. We fortuitously detect CO
J=3–2 emission from a z = 0.375 galaxy in the foreground cluster A370, and obtain a CO line luminosity of
L'(CO) > (8.95 ± 0.79) × 10^8 K km s^−1 pc^2 and a molecular gas mass of M(H_2) > (4.12 ± 0.36) × 10^9 M_☉, for a CO-to-H_2 conversion factor of 4.6M_☉ (K km s^−1 pc^2)^−1
Star Formation and Gas Kinematics of Quasar Host Galaxies at z~6: New Insights from ALMA
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [C II] 158 μm fine structure line and dust continuum emission from the host galaxies of five redshift 6 quasars. We also report complementary observations of 250 GHz dust continuum and CO (6-5) line emission from the z = 6.00 quasar SDSS J231038.88+185519.7 using the IRAM facilities. The ALMA observations were carried out in the extended array at 0.\u27\u277 resolution. We have detected the line and dust continuum in all five objects. The derived [C II] line luminosities are 1.6 × 109 to 8.7 × 109 L ☉ and the [C II]-to-FIR luminosity ratios are 2.9-5.1 ×10–4, which is comparable to the values found in other high-redshift quasar-starburst systems and local ultra-luminous infrared galaxies. The sources are marginally resolved and the intrinsic source sizes (major axis FWHM) are constrained to be 0.\u27\u273-0.\u27\u276 (i.e., 1.7-3.5 kpc) for the [C II] line emission and 0.\u27\u272-0.\u27\u274 (i.e., 1.2-2.3 kpc) for the continuum. These measurements indicate that there is vigorous star formation over the central few kpc in the quasar host galaxies. The ALMA observations also constrain the dynamical properties of the star-forming gas in the nuclear region. The intensity-weighted velocity maps of three sources show clear velocity gradients. Such velocity gradients are consistent with a rotating, gravitationally bound gas component, although they are not uniquely interpreted as such. Under the simplifying assumption of rotation, the implied dynamical masses within the [C II]-emitting regions are of order 1010-1011 M ☉. Given these estimates, the mass ratios between the supermassive black holes and the spheroidal bulge are an order of magnitude higher than the mean value found in local spheroidal galaxies, which is in agreement with results from previous CO observations of high redshift quasars
The Interstellar Medium Properties of Heavily Reddened Quasars & Companions at z~2.5 with ALMA & JVLA
We study the interstellar medium (ISM) properties of three heavily reddened
quasars at as well as three millimetre-bright companion galaxies
near these quasars. New JVLA and ALMA observations constrain the CO(1-0),
CO(7-6) and [CI]PP line emission as well as the far infrared to
radio continuum. The gas excitation and physical properties of the ISM are
constrained by comparing our observations to photo-dissociation region (PDR)
models. The ISM in our high-redshift quasars is composed of very high-density,
high-temperature gas which is already highly enriched in elements like carbon.
One of our quasar hosts is shown to be a close-separation (2 arcsec) major
merger with different line emission properties in the millimeter-bright galaxy
and quasar components. Low angular resolution observations of high-redshift
quasars used to assess quasar excitation properties should therefore be
interpreted with caution as they could potentially be averaging over multiple
components with different ISM conditions. Our quasars and their companion
galaxies show a range of CO excitation properties spanning the full extent from
starburst-like to quasar-like spectral line energy distributions. We compare
gas masses based on CO, CI and dust emission, and find that these can disagree
when standard assumptions are made regarding the values of ,
the gas-to-dust ratio and the atomic carbon abundances. We conclude that the
ISM properties of our quasars and their companion galaxies are diverse and
likely vary spatially across the full extent of these complex, merging systems.Comment: Accepted for publication in MNRAS (18 pages, 10 figures and 5 tables
A new twist to an old story: HE 0450-2958, and the ULIRG(optically bright QSO) transition hypothesis
We report on interferometric imaging of the CO J=1--0 and J=3--2 line
emission from the controversial QSO/galaxy pair HE 0450--2958. {\it The
detected CO J=1--0 line emission is found associated with the disturbed
companion galaxy not the luminous QSO,} and implies , which is \ga 30% of the dynamical mass in
its CO-luminous region. Fueled by this large gas reservoir this galaxy is the
site of an intense starburst with , placing
it firmly on the upper gas-rich/star-forming end of Ultra Luminous Infrared
Galaxies (ULIRGs, ). This makes HE 0450--2958 the
first case of extreme starburst and powerful QSO activity, intimately linked
(triggered by a strong interaction) but not coincident. The lack of CO emission
towards the QSO itself renews the controversy regarding its host galaxy by
making a gas-rich spiral (the typical host of Narrow Line Seyfert~1 AGNs) less
likely. Finally, given that HE 0450--2958 and similar IR-warm QSOs are
considered typical ULIRG(optically bright QSO) transition candidates, our
results raise the possibility that some may simply be {\it gas-rich/gas-poor
(e.g. spiral/elliptical) galaxy interactions} which ``activate'' an optically
bright unobscured QSO in the gas-poor galaxy, and a starburst in the gas-rich
one. We argue that such interactions may have gone largely unnoticed even in
the local Universe because the combination of tools necessary to disentagle the
progenitors (high resolution and S/N optical {\it and} CO imaging) became
available only recently.Comment: 25 pages, 5 figures, accepted for publication by The Astrophysical
Journa
CO J=2-1 line emission in cluster galaxies at z~1: fueling star formation in dense environments
We present observations of CO J=2-1 line emission in infrared-luminous
cluster galaxies at z~1 using the IRAM Plateau de Bure Interferometer. Our two
primary targets are optically faint, dust-obscured galaxies (DOGs) found to lie
within 2 Mpc of the centers of two massive (>10^14 Msun) galaxy clusters. CO
line emission is not detected in either DOG. We calculate 3-sigma upper limits
to the CO J=2-1 line luminosities, L'_CO < 6.08x10^9 and < 6.63x10^9 K km/s
pc^2. Assuming a CO-to-H_2 conversion factor derived for ultraluminous infrared
galaxies in the local Universe, this translates to limits on the cold molecular
gas mass of M_H_2 < 4.86x10^9 Msun and M_H_2 < 5.30x10^9 Msun. Both DOGs
exhibit mid-infrared continuum emission that follows a power-law, suggesting
that an AGN contributes to the dust heating. As such, estimates of the star
formation efficiencies in these DOGs are uncertain. A third cluster member with
an infrared luminosity, L_IR < 7.4x10^11 Lsun, is serendipitously detected in
CO J=2-1 line emission in the field of one of the DOGs located roughly two
virial radii away from the cluster center. The optical spectrum of this object
suggests that it is likely an obscured AGN, and the measured CO line luminosity
is L'_CO = (1.94 +/- 0.35)x10^10 K km/s pc^2, which leads to an estimated cold
molecular gas mass M_H_2 = (1.55+/-0.28)x10^10 Msun. A significant reservoir of
molecular gas in a z~1 galaxy located away from the cluster center demonstrates
that the fuel can exist to drive an increase in star-formation and AGN activity
at the outskirts of high-redshift clusters.Comment: 22 pages, 4 figures; accepted for publication in Ap
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