314 research outputs found
[CII] line emission in BRI1335-0417 at z=4.4
Using the 12m APEX telescope, we have detected redshifted emission from the
157.74micron [CII] line in the z=4.4074 quasar BRI1335-0417. The linewidth and
redshift are in good agreement with previous observations of high-J CO line
emission. We measure a [CII] line luminosity, L_[CII] = (16.4 +/- 2.6)x10^9
Lsun, making BRI~1335-0417 the most luminous, unlensed [CII] line emitter known
at high-redshift. The [CII]-to-FIR luminosity ratio of (5.3+/-0.8)x10^-4 is ~3x
higher than expected for an average object with a FIR luminosity L_FIR =
3.1x10^13 Lsun, if this ratio were to follow the trend observed in other
FIR-bright galaxies that have been detected in [CII] line emission. These new
data suggest that the scatter in the [CII]-to-FIR luminosity ratio could be
larger than previously expected for high luminosity objects. BR1335-0417 has a
similar FIR luminosity and [CII]/CO luminosity compared to local ULIRGS and
appears to be a gas-rich merger forming stars at a rate of a few thousand solar
masses per year.Comment: A&A accepte
Molecular Gas in Infrared Ultraluminous QSO Hosts
We report CO detections in 17 out of 19 infrared ultraluminous QSO (IR QSO)
hosts observed with the IRAM 30m telescope. The cold molecular gas reservoir in
these objects is in a range of 0.2--2.1 (adopting a
CO-to- conversion factor ). We find that the molecular gas properties of IR QSOs,
such as the molecular gas mass, star formation efficiency () and the CO (1-0) line widths, are indistinguishable
from those of local ultraluminous infrared galaxies (ULIRGs). A comparison of
low- and high-redshift CO detected QSOs reveals a tight correlation between
L and for all QSOs. This suggests that,
similar to ULIRGs, the far-infrared emissions of all QSOs are mainly from dust
heated by star formation rather than by active galactic nuclei (AGNs),
confirming similar findings from mid-infrared spectroscopic observations by
{\it Spitzer}. A correlation between the AGN-associated bolometric luminosities
and the CO line luminosities suggests that star formation and AGNs draw from
the same reservoir of gas and there is a link between star formation on
kpc scale and the central black hole accretion process on much smaller scales.Comment: 30 pages, 9 figures, accepted for publication in The Astrophysical
Journa
Weak 13CO in the Cloverleaf Quasar: evidence for a young, early generation starburst
Observations of 12CO at high redshift indicate rapid metal enrichment in the
nuclear regions of at least some galaxies in the early universe. However, the
enrichment may be limited to nuclei that are synthesized by short-lived massive
stars, excluding classical secondary nuclei like 13CO. Testing this idea, we
tentatively detect the 13CO J=3-2 line at a level of 0.3 Jy km/s toward the
Cloverleaf Quasar at redshift 2.5. This is the first observational evidence for
13CO at high redshift. The 12CO/13CO J=3-2 luminosity ratio is with at least 40
much higher than ratios observed in molecular clouds of the Milky Way and in
the ultraluminous galaxy Arp 220, but may be similar to that observed toward
NGC 6240. Large Velocity Gradient (LVG) models simulating seven 12CO
transitions and the 13CO line yield 12CO/13CO abundance ratios in excess of 100
for the Cloverleaf. It is possible that the measured ratio is affected by a
strong submillimeter radiation field, which reduces the contrast between the
13CO line and the background. It is more likely, however, that the ratio is
caused by a real deficiency of 13CO. A potential conflict with optical data,
indicating high abundances also for secondary nuclei in quasars of high
redshift, may be settled if the bulk of the CO emission is originating
sufficiently far from the active galactic nucleus.Comment: 7 pages, 5 figures, accepted for publication in A&A (Main Journal
Evidence for a clumpy, rotating gas disk in a submillimeter galaxy at z=4
We present Karl G. Jansky Very Large Array (VLA) observations of the CO(2-1)
emission in the z=4.05 submillimeter galaxy (SMG) GN20. These high-resolution
data allow us to image the molecular gas at 1.3 kpc resolution just 1.6 Gyr
after the Big Bang. The data reveal a clumpy, extended gas reservoir, 14 +/- 4
kpc in diameter, in unprecedented detail. A dynamical analysis shows that the
data are consistent with a rotating disk of total dynamical mass 5.4 +/- 2.4 X
10^11 M_sun. We use this dynamical mass estimate to constrain the CO-to-H_2
mass conversion factor (alpha_CO), finding alpha_CO=1.1 +/- 0.6 M_sun (K km
s^-1 pc^2)^-1. We identify five distinct molecular gas clumps in the disk of
GN20 with masses a few percent of the total gas mass, brightness temperatures
of 16-31K, and surface densities of >3,200-4,500 X (alpha_CO/0.8) M_sun pc^-2.
Virial mass estimates indicate they could be self-gravitating, and we constrain
their CO-to-H_2 mass conversion factor to be <0.2-0.7 M_sun (K km s^-1
pc^2)^-1. A multiwavelength comparison demonstrates that the molecular gas is
concentrated in a region of the galaxy that is heavily obscured in the
rest-frame UV/optical. We investigate the spatially-resolved gas excitation and
find that the CO(6-5)/CO(2-1) ratio is constant with radius, consistent with
star formation occuring over a large portion of the disk. We discuss the
implications of our results in the context of different fueling scenarios for
SMGs.Comment: 15 pages, 9 figures, accepted for publication in Ap
Deep observations of CO line emission from star-forming galaxies in a cluster candidate at z=1.5
We report results from a deep Jansky Very Large Array (JVLA) search for CO
1-0 line emission from galaxies in a candidate galaxy cluster at z~1.55 in the
COSMOS field. We target 4 galaxies with optical spectroscopic redshifts in the
range z=1.47-1.59. Two of these 4 galaxies, ID51613 and ID51813, are nominally
detected in CO line emission at the 3-4 sigma level. We find CO luminosities of
2.4x10^10 K km/s pc^2 and 1.3x10^10 K km/s pc^2, respectively. Taking advantage
from the clustering and 2-GHz bandwidth of the JVLA, we perform a search for
emission lines in the proximity of optical sources within the field of view of
our observations. We limit our search to galaxies with K<23.5 (AB) and
z_phot=1.2-1.8. We find 2 bright optical galaxies to be associated with
significant emission line peaks (>4 sigma) in the data cube, which we identify
with the CO line emission. To test the reliability of the line peaks found, we
performed a parallel search for line peaks using a Bayesian inference method.
Monte Carlo simulations show that such associations are statistically
significant, with probabilities of chance association of 3.5% and 10.7% for ID
51207 and ID 51380, respectively. Modeling of their optical/IR SEDs indicates
that the CO detected galaxies and candidates have stellar masses and SFRs in
the range (0.3-1.1)x10^11 M_sun and 60-160 M_sun/yr, with SFEs comparable to
that found in other star-forming galaxies at similar redshifts. By comparing
the space density of CO emitters derived from our observations with the space
density derived from previous CO detections at z~1.5, and with semi-analytic
predictions for the CO luminosity function, we suggest that the latter tend to
underestimate the number of CO galaxies detected at high-redshift. Finally, we
argue about the benefits of future blind CO searches in clustered fields with
upcoming submm/radio facilities.Comment: Accepted for publication in MNRAS. Abstract has been slightly
shortened compared to original pdf versio
The Molecular Gas Content of z = 3 Lyman Break Galaxies; Evidence of a non Evolving Gas Fraction in Main Sequence Galaxies at z > 2
We present observations of the CO[3-2] emission towards two massive and
infrared luminous Lyman Break Galaxies at z = 3.21 and z = 2.92, using the IRAM
Plateau de Bure Interferometer, placing first constraints on the molecular gas
masses (Mgas) of non-lensed LBGs. Their overall properties are consistent with
those of typical (Main-Sequence) galaxies at their redshifts, with specific
star formation rates ~1.6 and ~2.2 Gyr^(-1), despite their large infrared
luminosities L_IR ~2-3 x 10^12 Lsun derived from Herschel. With one plausible
CO detection (spurious detection probability of 10^(-3)) and one upper limit,
we investigate the evolution of the molecular gas-to-stellar mass ratio
(Mgas/M*) with redshift. Our data suggest that the steep evolution of Mgas/M*
of normal galaxies up to z~2 is followed by a flattening at higher redshifts,
providing supporting evidence for the existence of a plateau in the evolution
of the specific star formation rate at z > 2.5.Comment: Accepted for publication in ApJ
Resolving the dynamical mass of a z~1.3 QSO host galaxy using SINFONI and Laser Guide Star assisted Adaptive Optics
Recent studies of the tight scaling relations between the masses of
supermassive black holes and their host galaxies have suggested that in the
past black holes constituted a larger fraction of their host galaxies' mass.
However, these arguments are limited by selection effects and difficulties in
determining robust host galaxy masses at high redshifts. Here we report the
first results of a new, complementary diagnostic route: we directly determine a
dynamical host galaxy mass for the z=1.3 luminous quasar J090543.56+043347.3
through high-spatial-resolution (0.47", 4kpc FWHM) observations of the host
galaxy gas kinematics over 30x40 kpc using ESO/VLT/SINFONI with LGS/AO.
Combining our result of M_dyn = 2.05+1.68_0.74 x 10^11 M_sun (within a radius
5.25 +- 1.05 kpc) with M_BH,MgII = 9.02 \pm 1.43 x 10^8 M_sun, M_BH,Halpha =
2.83 +1.93-1.13 x 10^8 M_sun, we find that the ratio of black hole mass to host
galaxy dynamical mass for J090543.56+043347.3 matches the present-day relation
for M_BH vs. M_Bulge,Dyn, well within the IR scatter, deviating at most a
factor of two from the mean. J090543.56+043347.3 displays clear signs of an
ongoing tidal interaction and of spatially extended star formation at a rate of
50-100 M_sun/yr, above the cosmic average for a galaxy of this mass and
redshift. We argue that its subsequent evolution may move J090543.56+043347.3
even closer to the z=0 relation for M_BH vs. M_Bulge,Dyn. Our results support
the picture where any substantive evolution in these relations must occur prior
to z~1.3. Having demonstrated the power of this modelling approach we are
currently analyzing similar data on seven further objects to better constrain
such evolution.Comment: Accepted for publication in ApJ, 14 pages, 10 Figure
Measuring space-time variation of the fundamental constants with redshifted submillimetre transitions of neutral carbon
We compare the redshifts of neutral carbon and carbon monoxide in the
redshifted sources in which the fine structure transition of neutral carbon,
[CI], has been detected, in order to measure space-time variation of the
fundamental constants. Comparison with the CO rotational lines measures gives
the same combination of constants obtained from the comparison fine structure
line of singly ionised carbon, [CII]. However, neutral carbon has the distinct
advantage that it may be spatially coincident with the carbon monoxide, whereas
[CII] could be located in the diffuse medium between molecular clouds, and so
any comparison with CO could be dominated by intrinsic velocity differences.
Using [CI], we obtain a mean variation of dF/F = (-3.6 +/- 8.5) x 10^-5, over z
= 2.3 - 4.1, for the eight [CI] systems, which degrades to (-1.5+/- 11) x
10^-5, over z = 2.3 - 6.4 when the two [CII] systems are included. That is,
zero variation over look-back times of 10.8-12.8 Gyr. However, the latest
optical results indicate a spatial variation in alpha, which describes a dipole
and we see the same direction in dF/F. This trend is, however, due to a single
source for which the [CI] spectrum is of poor quality. This also applies to one
of the two [CII] spectra previously used to find a zero variation in
alpha^2/mu. Quantifying this, we find an anti-correlation between |dF/F| and
the quality of the carbon detection, as measured by the spectral resolution,
indicating that the typical values of >50 km/s, used to obtain a detection, are
too coarse to reliably measure changes in the constants. From the fluxes of the
known z > 1 CO systems, we predict that current instruments are incapable of
the sensitivities required to measure changes in the constants through the
comparison of CO and carbon lines. We therefore discuss in detail the use of
ALMA for such an undertaking ... ABRIDGEDComment: Accepted for publication in Section 3 - Cosmology (including clusters
of galaxies) of Astronomy and Astrophysic
Enhanced [CII] emission in a z=4.76 submillimetre galaxy
We present the detection of bright [CII] emission in the z=4.76 submillimetre
galaxy LESS J033229.4-275619 using the Atacama Pathfinder EXperiment. This
represents the highest redshift [CII] detection in a submm selected,
star-formation dominated system. The AGN contributions to the [CII] and
far-infrared (FIR) luminosities are small. We find an atomic mass derived from
[CII] comparable to the molecular mass derived from CO. The ratio of the [CII],
CO and FIR luminosities imply a radiation field strength G_0~10^3 and a density
~10^4 cm^-3 in a kpc-scale starburst, as seen in local and high redshift
starbursts. The high L_[CII]/L_FIR=2.4x10^-3 and the very high
L_[CII]/L_CO(1-0) ~ 10^4 are reminiscent of low metallicity dwarf galaxies,
suggesting that the highest redshift star-forming galaxies may also be
characterised by lower metallicities. We discuss the implications of a reduced
metallicity on studies of the gas reservoirs, and conclude that especially at
very high redshift, [CII] may be a more powerful and reliable tracer of the
interstellar matter than CO.Comment: 5 pages, 2 figures; accepted for publication in Astronomy &
Astrophysics Letter
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&
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