arXiv subjects

Roberto Neri

Publications and source records attributed to Roberto Neri.

At least 73 records · Page 4Linked to original sources

arXiv2016

SMA Observations of the Extended CO(6-5) Emission in the Starburst Galaxy NGC253

We present observations of the $^{12}$CO(6-5) line and 686GHz continuum emission in NGC253 with the Submillimeter Array at an angular resolution of ~4arcsec. The $^{12}$CO(6-5) emission is clearly detected along the disk and follows the distribution of the lower $^{12}$CO line transitions with little variations of the line ratios in it. A large-velocity gradient analysis suggests a two-temperature model of the molecular gas in the disk, likely dominated by a combination of low-velocity shocks and the disk wide PDRs. Only marginal $^{12}$CO(6-5) emission is detected in the vicinity of the expanding shells at the eastern and western edges of the disk. While the eastern shell contains gas even warmer (T$_{\rm kin}$>300~K) than the hot gas component (T$_{\rm kin}$=300K) of the disk, the western shell is surrounded by gas much cooler (T$_{\rm kin}$=60K) than the eastern shell but somewhat hotter than the cold gas component of the disk (for similar H$_2$ and CO column densities), indicative of different (or differently efficient) heating mechansisms. The continuum emission at 686GHz in the disk agrees well in shape and size with that at lower (sub-)millimeter frequencies, exhibiting a spectral index consistent with thermal dust emission. We find dust temperatures of ~10-30K and largely optically thin emission. However, our fits suggest a second (more optically thick) dust component at higher temperatures (T$_{\rm d}$>60K), similar to the molecular gas. We estimate a global dust mass of ~10$^6$Msun for the disk translating into a gas-to-dust mass ratio of a few hundred consistent with other nearby active galaxies.

astro-ph.GA↗

arXiv2015

Constraining the abundances of complex organics in the inner regions of solar-type protostars

The high abundances of Complex Organic Molecules (COMs) with respect to methanol, the most abundant COM, detected towards 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 towards the two low-mass protostars NGC1333-IRAS2A and -IRAS4A with the Plateau de Bure interferometer at an angular resolution of 2 arcsec, resulting in the first multi-line detection of the O-bearing species glycolaldehyde and ethanol and of the N-bearing species ethyl cyanide towards 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 COMs column densities. The COMs abundances with respect to methanol derived towards IRAS2A and IRAS4A are slightly, but not substantitally, lower than those derived from previous single-dish observations. The COMs 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.

astro-ph.SR↗

arXiv2014

First CO(17-16) emission line detected in a z > 6 quasar

We report the serendipitous detection of the CO(17-16) emission line toward the quasar SDSSJ114816.64+525150.3 (J1148) at redshift z = 6.4 obtained with the Plateau de Bure Interferometer. The CO(17-16) line is possibly contaminated by OH+ emission, that may account for ~ 35 - 60% of the total flux observed. Photo-Dissociation and X-ray Dominated Regions (PDRs and XDRs) models show that PDRs alone cannot reproduce the high luminosity of the CO(17-16) line relative to low-J CO transitions and that XDRs are required. By adopting a composite PDR+XDR model we derive molecular cloud and radiation field properties in the nuclear region of J1148. Our results show that highly excited CO lines represent a sensitive and possibly unique tool to infer the presence of X-ray faint or obscured supermassive black hole progenitors in high-z galaxies.

astro-ph.GA↗

arXiv2014

ALMA Observation of 158 micron [CII] Line and Dust Continuum of a z=7 Normally Star-forming Galaxy in the Epoch of Reionization

We present ALMA observations of the [CII] line and far-infrared (FIR) continuum of a normally star-forming galaxy in the reionization epoch, the z=6.96 Ly-alpha emitter (LAE) IOK-1. Probing to sensitivities of sigma_line = 240 micro-Jy/beam (40 km/s channel) and sigma_cont = 21 micro-Jy/beam, we found the galaxy undetected in both [CII] and continuum. Comparison of UV - FIR spectral energy distribution (SED) of IOK-1, including our ALMA limit, with those of several types of local galaxies (including the effects of the cosmic microwave background, CMB, on the FIR continuum) suggests that IOK-1 is similar to local dwarf/irregular galaxies in SED shape rather than highly dusty/obscured galaxies. Moreover, our 3 sigma FIR continuum limit, corrected for CMB effects, implies intrinsic dust mass M_dust < 6.4 x 10^7 M_sun, FIR luminosity L_FIR < 3.7 x 10^{10} L_sun (42.5 - 122.5 micron), total IR luminosity L_IR < 5.7 x 10^{10} L_sun (8 - 1000 micron) and dust-obscured star formation rate (SFR) < 10 M_sun/yr, if we assume that IOK-1 has a dust temperature and emissivity index typical of local dwarf galaxies. This SFR is 2.4 times lower than one estimated from the UV continuum, suggesting that < 29% of the star formation is obscured by dust. Meanwhile, our 3 sigma [CII] flux limit translates into [CII] luminosity, L_[CII] < 3.4 x 10^7 L_sun. Locations of IOK-1 and previously observed LAEs on the L_[CII] vs. SFR and L_[CII]/L_FIR vs. L_FIR diagrams imply that LAEs in the reionization epoch have significantly lower gas and dust enrichment than AGN-powered systems and starbursts at similar/lower redshifts, as well as local star-forming galaxies.

astro-ph.GA↗

arXiv2014

Search for [CII] emission in z=6.5-11 star-forming galaxies

We present the search for the [CII] emission line in three $z>6.5$ Lyman-alpha emitters (LAEs) and one J-Dropout galaxy using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and the Plateau de Bure Interferometer (PdBI). We observed three bright $z\sim6.5-7$ LAEs discovered in the SUBARU deep field (SDF) and the Multiple Imaged lensed $z\sim 11$ galaxy candidate found behind the galaxy cluster MACSJ0647.7+7015. For the LAEs IOK-1 ($z=6.965$), SDF J132415.7+273058 ($z=6.541$) and SDF J132408.3+271543 ($z=6.554$) we find upper limits for the [CII] line luminosity of $<2.05$, $<4.52$ and $<10.56\times10^{8}{\rm L}_{\odot}$ respectively. We find upper limits to the FIR luminosity of the galaxies using a spectral energy distribution template of the local galaxy NGC 6946 and taking into account the effects of the Cosmic Microwave Background on the mm observations. For IOK-1, SDF J132415.7+273058 and SDF J132408.3+271543 we find upper limits for the FIR luminosity of $<2.33$, $3.79$ and $7.72\times10^{11}{\rm L}_{\odot}$ respectively. For the lensed galaxy MACS0647-JD, one of the highest redshift galaxy candidate to date with $z_{\rm ph}=10.7^{+0.6}_{-0.4}$ we put an upper limit in the [CII] emission of $<1.36\times10^{8}\times(μ/15)^{-1}{\rm L}_{\odot}$ and an upper limit in the FIR luminosity of $<6.1\times10^{10}\times(μ/15)^{-1}{\rm L}_{\odot}$ (where $μ$ is the magnification factor). We explore the different conditions relevant for the search for [CII] emission in high redshift galaxies as well as the difficulties for future observations with ALMA and CCAT.

astro-ph.GA↗

arXiv2013

Star Formation and Gas Kinematics of Quasar Host Galaxies at z~6: New insights from ALMA

We present ALMA observations of the [C II] 158 micron 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. The ALMA observations were carried out in the extended array at 0.7" resolution. We have detected the line and dust continuum in all five objects. The derived [C II] line luminosities are 1.6x10^{9} to 8.8x10^{9} Lsun and the [C II]-to-FIR luminosity ratios are 3.0-5.6x10^{-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 0.3" to 0.6" (i.e., 1.7 to 3.5 kpc) for the [C II] line emission and 0.2" to 0.4" (i.e., 1.2 to 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 atomic gas in the starburst nuclei. 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 10^{10} to 10^{11} Msun. Given these estimates, the mass ratios between the SMBHs 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.

astro-ph.CO↗

arXiv2013

Millimeter Recombination Lines from LkHalpha 101

We present new millimeter observations of the ionized wind from the massive young stellar object LkHalpha101, made with the IRAM interferometer and 30m telescope. Several recombination lines, including higher order transitions, were detected for the first time at radio wavelengths in this source. From three alpha-transitions we derive an accurate value for the stellar velocity and, for the first time, an unambiguous expansion velocity of the wind which is 55 km/s, much slower than reported previously, and the mass loss rate is 1.8e-6 solar masses per year. The wide band continuum spectra and the interferometer visibilities show that the density of the wind falls off more steeply than compatible with constant-velocity expansion. We argue that these properties indicate that the wind is launched from a radially narrow region of the circumstellar disk, and we propose that slow speed and a steep density gradient are characteristic properties of the evolutionary phase where young stars of intermediate and high mass clear away the gaseous component of their accretion disks. The recombination lines are emitted close to local thermal equilibrium, but the higher order transitions appear systematically broader and weaker than expected, probably due to impact broadening. Finally, we show that LkHalpha101 shares many properties with MWC349, the only other stellar wind source where radio recombination lines have been detected, some of them masing. We argue that LkHalpha101 evades masing at millimeter wavelengths because of the disk's smaller size and unfavorable orientation. Some amplification may however be detectable at shorter wavelengths.

astro-ph.GA↗

arXiv2013

Water deuterium fractionation in the inner regions of two solar type protostars

The [HDO]/[H2O] ratio is a crucial parameter for probing the history of water formation. So far, it has been measured for only three solar type protostars and yielded different results, possibly pointing to a substantially different history in their formation. In the present work, we report new interferometric observations of the HDO 4 2,2 - 4 2,3 line for two solar type protostars, IRAS2A and IRAS4A, located in the NGC1333 region. In both sources, the detected HDO emission originates from a central compact unresolved region. Comparison with previously published interferometric observations of the H218$O 3 1,3 - 2 2,0 line shows that the HDO and H$_2$O lines mostly come from the same region. A non-LTE LVG analysis of the HDO and H218$O line emissions, combined with published observations, provides a [HDO]/[H2O] ratio of 0.3 - 8 % in IRAS2A and 0.5 - 3 % in IRAS4A. First, the water fractionation is lower than that of other molecules such as formaldehyde and methanol in the same sources. Second, it is similar to that measured in the solar type protostar prototype, IRAS16293-2422, and, surprisingly enough, larger than that measured in NGC1333 IRAS4B. {The comparison of the measured values towards IRAS2A and IRAS4A with the predictions of our gas-grain model GRAINOBLE gives similar conclusions to those for IRAS 16293, arguing that these protostars {share} a similar chemical history, although they are located in different clouds.

astro-ph.GA↗

arXiv2011

The ISM in distant star-forming galaxies: Turbulent pressure, fragmentation and cloud scaling relations in a dense gas disk at z=2.3

We have used the IRAM Plateau de Bure Interferometer and the Expanded Very Large Array to obtain a high resolution map of the CO(6-5) and CO(1-0) emission in the lensed, star-forming galaxy SMMJ2135-0102 at z=2.32. The kinematics of the gas are well described by a model of a rotationally-supported disk with an inclination-corrected rotation speed, v_rot = 320+/-25km/s, a ratio of rotational- to dispersion- support of v/sigma=3.5+/-0.2 and a dynamical mass of 6.0+/-0.5x10^10Mo within a radius of 2.5kpc. The disk has a Toomre parameter, Q=0.50+/-0.15, suggesting the gas will rapidly fragment into massive clumps on scales of L_J ~ 400pc. We identify star-forming regions on these scales and show that they are 10x denser than those in quiescent environments in local galaxies, and significantly offset from the local molecular cloud scaling relations (Larson's relations). The large offset compared to local molecular cloud linewidth-size scaling relations imply that supersonic turbulence should remain dominant on scales ~100x smaller than in the kinematically quiescent ISM of the Milky Way, while the molecular gas in SMMJ2135 is expected to be ~50x denser than that in the Milky Way on all scales. This is most likely due to the high external hydrostatic pressure we measure for the interstellar medium (ISM), P_tot/kB ~ (2+/-1)x10^7K/cm3. In such highly turbulent ISM, the subsonic regions of gravitational collapse (and star-formation) will be characterised by much higher critical densities, n_crit>=10^8/cm3, a factor ~1000x more than the quiescent ISM of the Milky Way.

astro-ph.CO↗

arXiv2011

Constraining Dust and Molecular Gas Properties in Lyman Alpha Blobs at z~3

In order to constrain the bolometric luminosities, dust properties and molecular gas content of giant Lyman alpha nebulae, the so-called Lyman alpha blobs, we have carried out a study of dust continuum and CO line emission in two well-studied representatives of this population at z ~ 3: a Lya blob discovered by its strong Spitzer MIPS 24um detection (LABd05; Dey et al. 2005) and the Steidel blob 1 (SSA22-LAB01; Steidel et al. 2000). We find that the spectral energy distribution of LABd05 is well described by an AGN-starburst composite template with L(FIR) = (4.0 +/- 0.5) x 10^12 Lsun, comparable to high-z sub-millimeter galaxies and ultraluminous infrared galaxies. New APEX/LABOCA 870um measurements rule out the reported SCUBA detection of the SSA22-LAB01 (S[850um] = 16.8 mJy) at the > 4sigma level. Consistent with this, ultra-deep Plateau de Bure Interferometer (PdBI) observations with ~2arcsec spatial resolution also fail to detect any 1.2mm continuum source down to ~0.45mJy per beam (3sigma). Combined with the existing (sub)mm observations in the literature, we conclude that the FIR luminosity of SSA22-LAB01 remains uncertain. No CO line is detected in either case down to integrated flux limits of (Snu dV) < 0.25--1.0 Jy km/s, indicating a modest molecular gas reservoir, M(H_2) < 1--3 x 10^10 Msun. The non-detections exclude, with high significance (12 sigma), the previous tentative detection of a CO(4-3) line in the SSA22-LAB01. The increased sensitivity afforded by ALMA will be critical in studying molecular gas and dust in these interesting systems.

astro-ph.CO↗

arXiv2011

Intermediate-mass hot cores at 500 AU: disks or outflows?

Observations with the Plateau de Bure Interferometer in the most extended configuration toward two intermediate-mass star-forming regions, IRAS22198+6336 and AFGL5142, reveal the presence of several complex organic molecules at ~500 AU scales, confirming the presence of hot cores in both regions. The hot cores are not rich in CN-bearing molecules, as often seen in massive hot cores, and are mainly traced by CH3CH2OH, (CH2OH)2, CH3COCH3, and CH3OH, with additionally CH3CHO, CH3OD and HCOOD for IRAS22198+6336, and C6H, and O13CS for AFGL5142. The emission of complex molecules is resolved down to sizes of ~300 and ~600 AU, for IRAS22198+6336 and AFGL5142, respectively, and most likely is tracing protostellar disks rather than flattened envelopes or toroids as usually found. This is specially clear for the case of IRAS22198+6336, where we detect a velocity gradient for all the mapped molecules perpendicular to the most chemically rich outflow of the region, yielding a dynamic mass >4 Msun. As for AFGL5142, the hot core emission is resolved into two elongated cores separated 1800 AU. A detailed comparison of the complex molecule peaks to the new CO(2-1) data and H2O maser data from literature suggests that also for AFGL5142 the complex molecules are mainly associated with disks, except for a faint and extended molecular emission found to the west, which is possibly produced in the interface between one of the outflows and the dense surrounding gas.

astro-ph.GA↗

arXiv2011

Massive young disks around Herbig Ae stars

Herbig Ae stars (HAe) are the precursors of Vega-type systems and, therefore, crucial objects in planet formation studies. Thus far, only a few disks associated with HAe stars have been studied using millimetre interferometers. Our aim is to determine the dust evolution and the lifetime of the disks associated with Herbig Ae stars. We imaged the continuum emission at 3 mm and 1.3 mm of the Herbig Ae/Be stars BD+61154, RR Tau, VY Mon and LkHa 198 using the Plateau de Bure Interferometer (PdBI). These stars are in the upper end of the stellar mass range of the Herbig Ae stars (stellar mass greater than 3 solar masses). Our measurements were used to complete the Spectral Energy Distribution (SED). The modelling of the SED, in particular the FIR-mm part, allow us to determine the masses and dust properties of these disks. We detected the disks associated with BD+61154, RR Tau and VY Mon with disk masses of 0.35 Msun, 0.05 Msun and 0.40 Msun respectively. The disk around LkHa 198 was not detected with an upper limit to the disk mass of 0.004 Msun. We detected, however, the disks associated with the younger stellar objects LkHa 198--IR and LkHa 198-mm that are located in the vicinity of LkHa 198. The fitting of the mm part of the SED reveal that the grains in the mid-plane of the disks around BD+61154, RR Tau and VY Mon have sizes of 1--1000 microns. Therefore, grains have not grown to centimetre sizes in these disks yet. These massive (M>3 Msun) and young (about 1 Myr) HAe stars are surrounded by massive (>0.04 Msun) disks with grains of micron-millimetre sizes. Although grain growth is proceeding in these disks, their evolutionary stage is prior to the formation of planetesimals. These disks are less evolved than those detected around T Tauri and Herbig Be stars.

astro-ph.SR↗

arXiv2011

A massive proto-cluster of galaxies at a redshift of z {\approx} 5.3

Massive clusters of galaxies have been found as early as 3.9 Billion years (z=1.62) after the Big Bang containing stars that formed at even earlier epochs. Cosmological simulations using the current cold dark matter paradigm predict these systems should descend from "proto-clusters" - early over-densities of massive galaxies that merge hierarchically to form a cluster. These proto-cluster regions themselves are built-up hierarchically and so are expected to contain extremely massive galaxies which can be observed as luminous quasars and starbursts. However, observational evidence for this scenario is sparse due to the fact that high-redshift proto-clusters are rare and difficult to observe. Here we report a proto-cluster region 1 billion years (z=5.3) after the Big Bang. This cluster of massive galaxies extends over >13 Mega-parsecs, contains a luminous quasar as well as a system rich in molecular gas. These massive galaxies place a lower limit of >4x10^11 solar masses of dark and luminous matter in this region consistent with that expected from cosmological simulations for the earliest galaxy clusters.

astro-ph.CO↗

arXiv2010

A Massive Molecular Gas Reservoir in the z=5.3 Submillimeter Galaxy AzTEC-3

We report the detection of CO 2-1, 5-4, and 6-5 emission in the highest-redshift submillimeter galaxy (SMG) AzTEC-3 at z=5.298, using the Expanded Very Large Array and the Plateau de Bure Interferometer. These observations ultimately confirm the redshift, making AzTEC-3 the most submillimeter-luminous galaxy in a massive z=5.3 protocluster structure in the COSMOS field. The strength of the CO line emission reveals a large molecular gas reservoir with a mass of 5.3e10 (alpha_CO/0.8) Msun, which can maintain the intense 1800 Msun/yr starburst in this system for at least 30 Myr, increasing the stellar mass by up to a factor of six in the process. This gas mass is comparable to `typical' z~2 SMGs, and constitutes >~80% of the baryonic mass (gas+stars) and 30%-80% of the total (dynamical) mass in this galaxy. The molecular gas reservoir has a radius of <4 kpc and likely consists of a `diffuse', low-excitation component, containing (at least) 1/3 of the gas mass (depending on the relative conversion factor alpha_CO), and a `dense', high-excitation component, containing ~2/3 of the mass. The likely presence of a substantial diffuse component besides highly-excited gas suggests different properties between the star-forming environments in z>4 SMGs and z>4 quasar host galaxies, which perhaps trace different evolutionary stages. The discovery of a massive, metal-enriched gas reservoir in a SMG at the heart of a large z=5.3 protocluster considerably enhances our understanding of early massive galaxy formation, pushing back to a cosmic epoch where the Universe was less than 1/12 of its present age.

astro-ph.CO↗

arXiv2010

Intense Star Formation within Resolved Compact Regions in a Galaxy at z=2.3

Massive galaxies in the early Universe have been shown to be forming stars at surprisingly high rates. Prominent examples are dust-obscured galaxies which are luminous when observed at sub-millimeter (sub-mm) wavelengths and which may be forming stars at rates upto 1,000Mo/yr. These intense bursts of star formation are believed to be driven by mergers between gas rich galaxies. However, probing the properties of individual star-forming regions within these galaxies is beyond the spatial resolution and sensitivity of even the largest telescopes at present. Here, we report observations of the sub-mm galaxy SMMJ2135-0102 at redshift z=2.3259 which has been gravitationally magnified by a factor of 32 by a massive foreground galaxy cluster lens. This cosmic magnification, when combined with high-resolution sub-mm imaging, resolves the star-forming regions at a linear scale of just ~100 parsecs. We find that the luminosity densities of these star-forming regions are comparable to the dense cores of giant molecular clouds in the local Universe, but they are ~100x larger and 10^7 times more luminous. Although vigorously star-forming, the underlying physics of the star formation processes at z~2 appears to be similar to that seen in local galaxies even though the energetics are unlike anything found in the present-day Universe.

astro-ph.CO↗

arXiv2009

Imaging Atomic and Highly Excited Molecular Gas in a z=6.42 Quasar Host Galaxy: Copious Fuel for an Eddington-Limited Starburst at the End of Cosmic Reionization

We have imaged CO(J=7-6) and CI(3P2-3P1) emission in the host galaxy of the z=6.42 quasar SDSS J114816.64+525150.3 (hereafter: J1148+5251) through observations with the Plateau de Bure Interferometer. The region showing CO(J=7-6) emission is spatially resolved, and its size of 5 kpc is in good agreement with earlier CO(J=3-2) observations. In combination with a revised model of the collisional line excitation in this source, this indicates that the highly excited molecular gas traced by the CO J=7-6 line is subthermally excited (showing only 58+/-8% of the CO J=3-2 luminosity), but not more centrally concentrated. We also detect CI(3P2-3P1) emission in the host galaxy of J1148+5251, but the line is too faint to enable a reliable size measurement. From the CI(3P2-3P1) line flux, we derive a total atomic carbon mass of M_CI=1.1x10^7 M_sun, which corresponds to ~5x10^-4 times the total molecular gas mass. We also searched for H2O(J_KaKc=2_12-1_01) emission, and obtained a sensitive line luminosity limit of L'_H2O<4.4x10^9 K kms pc^2, i.e., <15% of the CO(J=3-2) luminosity. The warm, highly excited molecular gas, atomic gas and dust in this quasar host at the end of cosmic reionization maintain an intense starburst that reaches surface densities as high as predicted by (dust opacity) Eddington limited star formation over kiloparsec scales.

astro-ph.CO↗

arXiv2008

Testing the Evolutionary Link Between Submillimetre Galaxies and Quasars: CO Observations of QSOs at z~2

We have used the IRAM Plateau de Bure mm interferometer and the UKIRT 1-5 um Imager Spectrometer to test the connection between the major phases of spheroid growth and nuclear accretion by mapping CO emission in nine submm-detected QSOs at z=1.7-2.6 with black hole (BH) masses derived from near-infrared spectroscopy. With a previously published QSO, we present sensitive CO(3-2) observations of 10 submm-detected QSOs selected at the epoch of peak activity in both QSOs and submm galaxies (SMGs). CO is detected in 5/6 very optically luminous (M_B~-28) submm-detected QSOs with BH masses M_BH~10^9-10^10 Msun, confirming the presence of large gas reservoirs of M_gas~3.4x10^10 Msun. However, we find that their BH masses are ~30 times too large and their surface density is ~300 times too small to be related to typical SMGs in an evolutionary sequence. Conversely, we measure weaker CO emission in four fainter (M_B~-25) submm-detected QSOs with properties, BH masses (M_BH~5x10^8 Msun), and surface densities similar to SMGs. These QSOs appear to lie near the local M_BH/M_sph relation, making them plausible `transition objects' in the proposed evolutionary sequence linking QSOs to the formation of massive young galaxies and BHs at high-redshift. We show that SMGs have a higher incidence of bimodal CO line profiles than seen in our QSO sample, which we interpret as an effect of their relative inclinations, with the QSOs seen more face-on. Finally, we find that the gas masses of the four fainter submm-detected QSOs imply that their star formation episodes could be sustained for ~10 Myr, and are consistent with representing a phase in the formation of massive galaxies which overlaps a preceding SMG starburst phase, before subsequently evolving into a population of present-day massive ellipticals. [abridged]

astro-ph↗

arXiv2007

Detection of Emission from the CN Radical in the Cloverleaf Quasar at z=2.56

We report the detection of CN(N=3-2) emission towards the Cloverleaf quasar (z=2.56) based on observations with the IRAM Plateau de Bure Interferometer. This is the first clear detection of emission from this radical at high redshift. CN emission is a tracer of dense molecular hydrogen gas (n(H2) > 10^4 cm^{-3}) within star-forming molecular clouds, in particular in regions where the clouds are affected by UV radiation. The HCN/CN intensity ratio can be used as a diagnostic for the relative importance of photodissociation regions (PDRs) in a source, and as a sensitive probe of optical depth, the radiation field, and photochemical processes. We derive a lensing-corrected CN(N=3-2) line luminosity of L'(CN(3-2) = (4.5 +/- 0.5) x 10^9 K km/s pc^2. The ratio between CN luminosity and far-infrared luminosity falls within the scatter of the same relationship found for low-z (ultra-) luminous infrared galaxies. Combining our new results with CO(J=3-2) and HCN(J=1-0) measurements from the literature and assuming thermal excitation for all transitions, we find a CO/CN luminosity ratio of 9.3 +/- 1.9 and a HCN/CN luminosity ratio of 0.95 +/- 0.15. However, we find that the CN(N=3-2) line is likely only subthermally excited, implying that those ratios may only provide upper limits for the intrinsic 1-0 line luminosity ratios. We conclude that, in combination with other molecular gas tracers like CO, HCN, and HCO+, CN is an important probe of the physical conditions and chemical composition of dense molecular environments at high redshift.

astro-ph↗