ABSTRACT The high abundances of Complex Organic Molecules (COMs) with respect to methanol, the most abundant COM, detected toward low-mass protostars, tend to be underpredicted by astrochemical ...models. This discrepancy might come from the large beam of the single-dish telescopes, encompassing several components of the studied protostar, commonly used to detect COMs. To address this issue, we have carried out multi-line observations of methanol and several COMs toward the two low-mass protostars NGC 1333-IRAS 2A and -IRAS 4A with the Plateau de Bure interferometer at an angular resolution of 2″, resulting in the first multi-line detection of the O-bearing species glycolaldehyde and ethanol and of the N-bearing species ethyl cyanide toward low-mass protostars other than IRAS 16293. The high number of detected transitions from COMs (more than 40 methanol transitions for instance) allowed us to accurately derive the source size of their emission and the COM column densities. The COM abundances with respect to methanol derived toward IRAS 2A and IRAS 4A are slightly, but not substantitally, lower than those derived from previous single-dish observations. The COM abundance ratios do not vary significantly with the protostellar luminosity, over five orders of magnitude, implying that low-mass hot corinos are quite chemically rich as high-mass hot cores. Astrochemical models still underpredict the abundances of key COMs, such as methyl formate or di-methyl ether, suggesting that our understanding of their formation remains incomplete.
Among more than 200 quasars known at z 6, only one object, J0100+2802 (z = 6.327), was found hosting a >1010 M supermassive black hole. In order to investigate the host galaxy properties of ...J0100+2802, we performed multi-band ALMA observations, aiming at mapping the dust continuum, C ii and CO(6-5) emission lines with subkiloparsec scale resolution, as well as detecting high-J CO lines in CO(11-10), CO(10-9), and CO(7-6). The galaxy size is measured to be Rmajor = 3.6 0.2 kpc from the high-resolution continuum observations. No ordered motion on kiloparsec scales was found in either the C ii or the CO(6-5) emission. The velocity dispersion is measured to be 161 7 km s−1, which is about three times smaller than that estimated from the local M- relation. In addition, we found that the CO emission is more concentrated (a factor of 1.8 0.4) than the C ii emission. Together with CO(2-1) detected by the Very Large Array (VLA), we measured the CO spectral line energy distribution, which is best fit by a two-component model that includes a cool component at ∼24 K with a density of cm−3, and a warm component at ∼224 K with a density of cm−3. We also fit the dust continuum with a graybody model. This indicated that the continuum has either a high dust emissivity β 2 or a hot dust temperature Tdust 60 K, or a combination of these two factors. The highly excited CO emission and hot dust temperature suggest that the powerful active galactic nucleus in J0100+2802 could contribute to the gas and dust heating, but future observations are needed to confirm this.
Abstract
Distortions of the observed cosmic microwave background provide a direct measurement of the microwave background temperature at redshifts from 0 to 1 (refs.
1,2
). Some additional ...background temperature estimates exist at redshifts from 1.8 to 3.3 based on molecular and atomic line-excitation temperatures in quasar absorption-line systems, but are model dependent
3
. No deviations from the expected (1 +
z
) scaling behaviour of the microwave background temperature have been seen
4
, but the measurements have not extended deeply into the matter-dominated era of the Universe at redshifts
z
> 3.3. Here we report observations of submillimetre line absorption from the water molecule against the cosmic microwave background at
z
= 6.34 in a massive starburst galaxy, corresponding to a lookback time of 12.8 billion years (ref.
5
). Radiative pumping of the upper level of the ground-state ortho-H
2
O(1
10
–1
01
) line due to starburst activity in the dusty galaxy HFLS3 results in a cooling to below the redshifted microwave background temperature, after the transition is initially excited by the microwave background. This implies a microwave background temperature of 16.4–30.2 K (1
σ
range) at
z
= 6.34, which is consistent with a background temperature increase with redshift as expected from the standard ΛCDM cosmology
4
.
We report the detection of CO(J = 2 → 1) emission from three massive dusty starburst galaxies at z > 5 through molecular line scans in the NSF's Karl G. Jansky Very Large Array (VLA) CO Luminosity ...Density at High Redshift (COLDz) survey. Redshifts for two of the sources, HDF 850.1 (z = 5.183) and AzTEC-3 (z = 5.298), were previously known. We revise a previous redshift estimate for the third source GN10 (z = 5.303), which we have independently confirmed through detections of CO J = 1 → 0, 5 → 4, 6 → 5, and C ii 158 m emission with the VLA and the NOrthern Extended Milllimeter Array. We find that two currently independently confirmed CO sources in COLDz are "optically dark", and that three of them are dust-obscured galaxies at z > 5. Given our survey area of ∼60 arcmin2, our results appear to imply a ∼6-55 times higher space density of such distant dusty systems within the first billion years after the Big Bang than previously thought. At least two of these z > 5 galaxies show star formation rate surface densities consistent with so-called "maximum" starbursts, but we find significant differences in CO excitation between them. This result may suggest that different fractions of the massive gas reservoirs are located in the dense, star-forming nuclear regions-consistent with the more extended sizes of the C ii emission compared to the dust continuum and higher C ii-to-far-infrared luminosity ratios in those galaxies with lower gas excitation. We thus find substantial variations in the conditions for star formation between z > 5 dusty starbursts, which typically have dust temperatures that are ∼57% 25% warmer than starbursts at z = 2-3 due to their enhanced star formation activity.
Abstract
We report the detection of 23 OH
+
1 → 0 absorption, emission, or P-Cygni-shaped lines and CO(
J
= 9→8) emission lines in 18 Herschel-selected
z
= 2–6 starburst galaxies with the Atacama ...Large Millimeter/submillimeter Array and the NOrthern Extended Millimeter Array, taken as part of the Gas And Dust Over cosmic Time Galaxy Survey. We find that the CO(
J
= 9→8) luminosity is higher than expected based on the far-infrared luminosity when compared to nearby star-forming galaxies. Together with the strength of the OH
+
emission components, this may suggest that shock excitation of warm, dense molecular gas is more prevalent in distant massive dusty starbursts than in nearby star-forming galaxies on average, perhaps due to an impact of galactic winds on the gas. OH
+
absorption is found to be ubiquitous in massive high-redshift starbursts, and is detected toward 89% of the sample. The majority of the sample shows evidence for outflows or inflows based on the velocity shifts of the OH
+
absorption/emission, with a comparable occurrence rate of both at the resolution of our observations. A small subsample appears to show outflow velocities in excess of their escape velocities. Thus, starburst-driven feedback appears to be important in the evolution of massive galaxies in their most active phases. We find a correlation between the OH
+
absorption optical depth and the dust temperature, which may suggest that warmer starbursts are more compact and have higher cosmic-ray energy densities, leading to more efficient OH
+
ion production. This is in agreement with a picture in which these high-redshift galaxies are “scaled-up” versions of the most intense nearby starbursts.
ABSTRACT We present the rationale for and the observational description of ASPECS: the ALMA SPECtroscopic Survey in the Hubble Ultra-Deep Field (UDF), the cosmological deep field that has the deepest ...multi-wavelength data available. Our overarching goal is to obtain an unbiased census of molecular gas and dust continuum emission in high-redshift (z > 0.5) galaxies. The ∼1′ region covered within the UDF was chosen to overlap with the deepest available imaging from the Hubble Space Telescope. Our ALMA observations consist of full frequency scans in band 3 (84-115 GHz) and band 6 (212-272 GHz) at approximately uniform line sensitivity ( 2 × 109 K km s−1 pc2), and continuum noise levels of 3.8 Jy beam−1 and 12.7 Jy beam−1, respectively. The molecular surveys cover the different rotational transitions of the CO molecule, leading to essentially full redshift coverage. The C ii emission line is also covered at redshifts . We present a customized algorithm to identify line candidates in the molecular line scans and quantify our ability to recover artificial sources from our data. Based on whether multiple CO lines are detected, and whether optical spectroscopic redshifts as well as optical counterparts exist, we constrain the most likely line identification. We report 10 (11) CO line candidates in the 3 mm (1 mm) band, and our statistical analysis shows that <4 of these (in each band) are likely spurious. Less than one-third of the total CO flux in the low-J CO line candidates are from sources that are not associated with an optical/NIR counterpart. We also present continuum maps of both the band 3 and band 6 observations. The data presented here form the basis of a number of dedicated studies that are presented in subsequent papers.
ABSTRACT In this paper we use ASPECS, the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field in band 3 and band 6, to place blind constraints on the CO luminosity function and the evolution of ...the cosmic molecular gas density as a function of redshift up to z ∼ 4.5. This study is based on galaxies that have been selected solely through their CO emission and not through any other property. In all of the redshift bins the ASPECS measurements reach the predicted "knee" of the CO luminosity function (around 5 × 109 K km s−1 pc2). We find clear evidence of an evolution in the CO luminosity function with respect to z ∼ 0, with more CO-luminous galaxies present at z ∼ 2. The observed galaxies at z ∼ 2 also appear more gas-rich than predicted by recent semi-analytical models. The comoving cosmic molecular gas density within galaxies as a function of redshift shows a drop by a factor of 3-10 from z ∼ 2 to z ∼ 0 (with significant error bars), and possibly a decline at z > 3. This trend is similar to the observed evolution of the cosmic star formation rate density. The latter therefore appears to be at least partly driven by the increased availability of molecular gas reservoirs at the peak of cosmic star formation (z ∼ 2).
The host galaxy of the quasar SDSS J114816.64+525150.3 (at redshift z = 6.42, when the Universe was less than a billion years old) has an infrared luminosity of 2.2 x 10(13) times that of the Sun, ...presumably significantly powered by a massive burst of star formation. In local examples of extremely luminous galaxies, such as Arp 220, the burst of star formation is concentrated in a relatively small central region of <100 pc radius. It is not known on which scales stars are forming in active galaxies in the early Universe, at a time when they are probably undergoing their initial burst of star formation. We do know that at some early time, structures comparable to the spheroidal bulge of the Milky Way must have formed. Here we report a spatially resolved image of C ii emission of the host galaxy of J114816.64+525150.3 that demonstrates that its star-forming gas is distributed over a radius of about 750 pc around the centre. The surface density of the star formation rate averaged over this region is approximately 1,000 year(-1) kpc(-2). This surface density is comparable to the peak in Arp 220, although about two orders of magnitude larger in area. This vigorous star-forming event is likely to give rise to a massive spheroidal component in this system.
Full text
Available for:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report Atacama Large Millimeter/submillimeter Array observations of CO(8-7), (9-8), , and and NOrthern Extended Millimeter Array observations of CO(5-4), (6-5), (12-11), and (13-12) toward the z = ...6.003 quasar SDSS J231038.88+185519.7, aiming to probe the physical conditions of the molecular gas content of this source. We present the best sampled CO spectral line energy distribution (SLED) at z = 6.003, and analyzed it with the radiative transfer code MOLPOP-CEP. Fitting the CO SLED to a one-component model indicates a kinetic temperature Tkin = 228 K, molecular gas density ) = 4.75, and CO column density ; although, a two-component model better fits the data. In either case, the CO SLED is dominated by a "warm" and "dense" component. Compared to samples of local (Ultra) Luminous Infrared Galaxies, starburst galaxies, and high-redshift submillimeter galaxies, J2310+1855 exhibits higher CO excitation at (J ≥ 8), like other high-redshift quasars. The high CO excitation, together with the enhanced , , and ratios, suggests that besides the UV radiation from young massive stars, other mechanisms such as shocks, cosmic-rays, and X-rays might also be responsible for the heating and ionization of the molecular gas. In the nuclear region probed by the molecular emissions lines, any of these mechanisms might be present due to the powerful quasar and the starburst activity.
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