CO Line Emission Research Articles

Molecular gas in the central region of NGC 7213

We present a multi-wavelength study (from X-ray to mm) of the nearby low-luminosity active galactic nucleus NGC 7213. We combine the information from the different bands to characterise the source in terms of contribution from the AGN and the host-galaxy interstellar medium. This approach allows us to provide a coherent picture of the role of the AGN and its impact, if any, on the star formation and molecular gas properties of the host galaxy. We focused our study on archival ALMA Cycle 1 observations, where the CO(2–1) emission line has been used as a tracer of the molecular gas. Using the 3DBAROLO code on ALMA data, we performed the modelling of the molecular gas kinematics traced by the CO(2–1) emission, finding a rotationally dominated pattern. The molecular gas mass of the host galaxy was estimated from the integrated CO(2–1) emission line obtained with APEX data, assuming an αCO conversion factor. Had we used the ALMA data, we would have underestimated the gas masses by a factor ∼3, given the filtering out of the large-scale emission in interferometric observations. We also performed a complete X-ray spectral analysis on archival observations, revealing a relatively faint and unobscured AGN. The AGN proved to be too faint to significantly affect the properties of the host galaxy, such as star formation activity and molecular gas kinematics and distribution.

Dense gas in a giant molecular filament

Context. Recent surveys of the Galactic plane in the dust continuum and CO emission lines reveal that large (≳50 pc) and massive (≳105 M⊙) filaments, know as giant molecular filaments (GMFs), may be linked to Galactic dynamics and trace the mid-plane of the gravitational potential in the Milky Way. Yet our physical understanding of GMFs is still poor. Aims. We investigate the dense gas properties of one GMF, with the ultimate goal of connecting these dense gas tracers with star formation processes in the GMF. Methods. We imaged one entire GMF located at l ~ 52–54° longitude, GMF54 (~68 pc long), in the empirical dense gas tracers using the HCN(1–0), HNC(1–0), and HCO+(1–0) lines, and their 13C isotopologue transitions, as well as the N2H+(1–0) line. We studied the dense gas distribution, the column density probability density functions (N-PDFs), and the line ratios within the GMF. Results. The dense gas molecular transitions follow the extended structure of the filament with area filling factors between 0.06 and 0.28 with respect to 13CO(1–0). We constructed the N-PDFs of H2 for each of the dense gas tracers based on their column densities and assumed uniform abundance. The N-PDFs of the dense gas tracers appear curved in log–log representation, and the HCO+ N-PDF has the flattest power-law slope index. Studying the N-PDFs for sub-regions of GMF54, we found an evolutionary trend in the N-PDFs that high-mass star-forming and photon-dominated regions have flatter power-law indices. The integrated intensity ratios of the molecular lines in GMF54 are comparable to those in nearby galaxies. In particular, the N2H+/13CO ratio, which traces the dense gas fraction, has similar values in GMF54 and all nearby galaxies except Ultraluminous Infrared Galaxies. Conclusions. As the largest coherent cold gaseous structure in our Milky Way, GMFs, are outstanding candidates for connecting studies of star formation on Galactic and extragalactic scales. By analyzing a complete map of the dense gas in a GMF we have found that: (1) the dense gas N-PDFs appear flatter in more evolved regions and steeper in younger regions, and (2) its integrated dense gas intensity ratios are similar to those of nearby galaxies.

Massive molecular gas reservoir around the central AGN in the CARLA J1103 + 3449 cluster at z = 1.44

Passive early-type galaxies dominate cluster cores at z ≲ 1.5. At higher redshift, cluster core galaxies are observed to have on-going star-formation, which is fueled by cold molecular gas. We measured the molecular gas reservoir of the central region around the radio-loud active galactic nucleus (AGN) in the cluster CARLA J1103 + 3449 at z = 1.44 using NOEMA. The AGN synchrotron emission dominates the continuum emission at 94.48 GHz, and we measured its flux at the AGN position and at the position of two radio jets. Combining our measurements with published results over the range 4.71–94.5 GHz, and assuming Ssynch ∝ ν−α, we obtain a flat spectral index of α = 0.14 ± 0.03 for the AGN core emission, and a steeper index of α = 1.43 ± 0.04 and α = 1.15 ± 0.04 at positions close to the western and eastern lobes, respectively. The total spectral index is α = 0.92 ± 0.02 over the range 73.8 MHz–94.5 GHz. We detect two CO(2–1) emission lines, both blueshifted with respect to the AGN. Their emission corresponds to two regions, ~17 kpc southeast and ~14 kpc southwest of the AGN, not associated with galaxies. In these two regions, we find a total massive molecular gas reservoir of Mgastot = 3.9 ± 0.4 × 1010 M⊙, which dominates (≳60%) the central total molecular gas reservoir. These results can be explained by massive cool gas flows in the center of the cluster. The AGN early-type host is not yet quenched; its star formation rate is consistent with being on the main sequence of star-forming galaxies in the field (star formation rate ~30–140 M⊙ yr−1), and the cluster core molecular gas reservoir is expected to feed the AGN and the host star formation before quiescence. The other confirmed cluster members show star formation rates at ~2σ below the field main sequence at similar redshifts and do not have molecular gas masses larger than galaxies of similar stellar mass in the field.

ALMA Deep Field in SSA22

Deep surveys with the Atacama Large Millimeter Array (ALMA) have uncovered a population of dusty star-forming galaxies which are faint or even undetected at optical to near-infrared wavelengths. Their faintness at short wavelengths makes the detailed characterization of the population challenging. Here we present a spectroscopic redshift identification and a characterization of one of these near-infrared-dark galaxies discovered by an ALMA deep survey. The detection of [C I](1–0) and CO(4–3) emission lines determines the precise redshift of the galaxy, ADF22.A2, to be z = 3.9913 ± 0.0008. On the basis of a multi-wavelength analysis, ADF22.A2 is found to be a massive, star-forming galaxy with a stellar mass of M∗ = 1.1−0.6+1.3 × 1011 M⊙ and SFR = 430−150+230 M⊙ yr−1. The molecular gas mass was derived to be M(H2)[CI] = (5.9 ± 1.5)×1010 M⊙, indicating a gas fraction of ≈35%, and the ratios of L[CI](1−0)/LIR and L[CI](1−0)/LCO(4−3) suggest that the nature of the interstellar medium in ADF22.A2 is in accordance with those of other bright submillimeter galaxies. The properties of ADF22.A2, including the redshift, star-formation rate, stellar mass, and depletion time scale (τdep ≈ 0.1−0.2 Gyr), also suggest that ADF22.A2 has the characteristics expected for the progenitors of quiescent galaxies at z ≳ 3. Our results demonstrate the power of ALMA contiguous mapping and line scan, which help us to obtain an unbiased view of galaxy formation in the early Universe.

Cold molecular gas and free–free emission from hot, dust-obscured galaxies at z ∼ 3

ABSTRACT We report on observations of redshifted CO(1–0) line emission and observed-frame $\rm \sim 30\,$GHz radio continuum emission from five ultra-luminous, mid-IR selected hot, Dust-Obscured Galaxies (Hot DOGs) at $z\rm \gtrsim 3$ using the Karl G. Jansky Very Large Array. We detect CO(1–0) line emission in all five Hot DOGs, with one of them at high signal-to-noise ratio. We analyse FIR-radio spectral energy distributions, including dust, free–free, and synchrotron emission for the galaxies. We find that most of the $\rm 115\,$ GHz rest-frame continuum is mostly due to synchrotron or free–free emission, with only a potentially small contribution from thermal emission. We see a deficit in the rest-frame $\rm 115\,$ GHz continuum emission compared to dusty star-forming galaxies and sub-millimetre galaxies (SMGs) at high redshift, suggesting that Hot DOGs do not have similar cold gas reserves compared with star-forming galaxies. One target, W2305−0039, is detected in the FIRST $\rm 1.4\, GHz$ survey, and is likely to possess compact radio jets. We compare to the FIR–radio correlation, and find that at least half of the Hot DOGs in our sample are radio-quiet with respect to normal galaxies. These findings suggest that Hot DOGs have comparably less cold molecular gas than star-forming galaxies at lower, $z\rm \sim 2$ redshifts, and are dominated by powerful, yet radio-quiet AGN.

Cosmic evolution of molecular gas mass density from an empirical relationship between L1.4 GHz and L′CO

ABSTRACT Historically, GHz radio emission has been used extensively to characterize the star-formation activity in galaxies. In this work, we look for empirical relationships amongst the radio luminosity, the infrared luminosity, and the CO-based molecular gas mass. We assemble a sample of 278 nearby galaxies with measurements of radio continuum and total infrared emission, and the 12CO J = 1–0 emission line. We find a correlation between the radio continuum and the CO emission line (with a scatter of 0.36 dex), in a large sample of different kinds of galaxies. Making use of this correlation, we explore the evolution of the molecular gas mass function and the cosmological molecular gas mass density in six redshift bins up to z = 1.5. These results agree with previous semi-analytic predictions and direct measurements: the cosmic molecular gas density increases up to z = 1.5. In addition, we find a single plane across five orders of magnitude for the explored luminosities, with a scatter of 0.27 dex. These correlations are sufficiently robust to be used for samples where no CO measurements exist.

Linking the small-scale relativistic winds and the large-scale molecular outflows in the z = 1.51 lensed quasar HS 0810+2554

ABSTRACT We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the quadruply lensed z = 1.51 quasar HS 0810+2554 which provide useful insight on the kinematics and morphology of the CO molecular gas and the ∼ 2 mm-continuum emission in the quasar host galaxy. Lens modelling of the mm-continuum and the spectrally integrated CO(J = 3→2) images indicates that the source of the mm-continuum has an eccentricity of e ∼ 0.9 with a size of ∼1.6 kpc and the source of line emission has an eccentricity of e ∼ 0.7 with a size of ∼1 kpc. The spatially integrated emission of the CO(J = 2→1) and CO(J = 3→2) lines shows a triple peak structure with the outer peaks separated by Δv21 = 220 ± 19 km s−1 and Δv32 = 245 ± 28 km s−1, respectively, suggesting the presence of rotating molecular CO line emitting gas. Lensing inversion of the high spatial resolution images confirms the presence of rotation of the line emitting gas. Assuming a conversion factor of αCO = 0.8 M⊙ (K km s−1 pc2)−1 we find the molecular gas mass of HS 0810+2554 to be MMol = (5.2 ± 1.5)/μ32 × 1010 M⊙, where μ32 is the magnification of the CO(J = 3→2) emission. We report the possible detection, at the 3.0–4.7σ confidence level, of shifted CO(J = 3→2) emission lines of high-velocity clumps of CO emission with velocities up to 1702 km s−1. We find that the momentum boost of the large-scale molecular wind is below the value predicted for an energy-conserving outflow given the momentum flux observed in the small-scale ultrafast outflow.

ALMA Imaging of the CO (7–6) Line Emission in the Submillimeter Galaxy LESS 073 at z = 4.755*

Abstract In this paper we present our imaging observations on the CO (7−6) line and its underlying continuum emission of the young submillimeter galaxy LESS 073 at redshift 4.755, using the Atacama Large Millimeter/submillimeter Array. At the achieved resolution of ∼ (8 × 6 kpc2), the CO (7−6) emission is largely unresolved (with a deconvolved size of ), and the continuum emission is totally unresolved. The CO (7−6) line emission has an integrated flux of 0.86 ± 0.08 Jy km s−1, and a line width of 343 ± 40 km s−1. The continuum emission has a flux density of 0.51 mJy. By fitting the observed far-infrared spectral energy distribution (SED) of LESS 073 with a single-temperature modified blackbody function, we obtained a dust temperature K, 60–100 μm flux density ratio , and total infrared luminosity . The SED-fit-based is consistent with those estimated from various line ratios as advocated by our earlier work, indicating that the proposed line-ratio-based method can be used to practically derive for high-z sources. The total molecular gas mass of LESS 073 is , and the inferred gas depletion time is about 43 Myr.

Atacama Cosmology Telescope: Dusty Star-forming Galaxies and Active Galactic Nuclei in the Equatorial Survey

Abstract We present a catalog of 510 radio-loud active galactic nuclei (AGNs, primarily blazars) and 287 dusty star-forming galaxies (DSFGs) detected by the Atacama Cosmology Telescope at significance in frequency bands centered on 148 GHz (2 mm), 218 GHz (1.4 mm), and 277 GHz (1.1 mm), from a 480 deg2 strip centered at R.A. 00h on the celestial equator with additional 360 deg2 shallower auxiliary fields at other longitudes. The combination of the deepest available 218 GHz wide-field imaging, our 277 GHz data, and multiband filtering results in the most sensitive wide-field millimeter-wave DSFG selection to date, with rms noise level referenced to 218 GHz reaching below 2 mJy. We have developed new techniques to remove Galactic contamination (including evidence for CO (2−1) line emission) from the extragalactic catalog, yielding a catalog of 321 Galactic sources in addition to the extragalactic catalog. We employ a new flux debiasing method that accounts for the heterogeneous sample selection in the presence of Galactic cuts. We present the spectral properties and source counts of the AGNs and DSFGs. The DSFG spectra depart from the Rayleigh–Jeans regime of an optically thin modified blackbody between 218 and 277 GHz, consistent with optically thick emission or an additional cold dust component. For AGNs with 148 and 218 GHz flux density >50 mJy, we estimate the interyear rms fractional deviation in flux density due to source variability to be 40% with a 0.98 interband correlation coefficient. We provide source counts for AGNs in the range of 8–2870 mJy and for DSFGs in the range of 8–90 mJy. Our DSFG counts probe both the brighter, lensed population and the fainter, unlensed population. At 277 GHz we report the first measurements of source counts at these flux densities, finding an excess above most model count predictions. Finally, we present 30 of the brightest DSFGs that were selected for multifrequency study as candidate high-z lensed systems.

SMM J04135+10277: a distant QSO–starburst system caught by ALMA

ABSTRACT The gas content of galaxies is a key factor for their growth, starting from star formation and black hole accretion to galaxy mergers. Thus, characterizing its properties through observations of tracers like the CO emission line is of big importance in order to understand the bigger picture of galaxy evolution. We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of dust continuum, CO(5–4) and CO(8–7) line emission in the quasar–star-forming companion system SMM J04135+10277 (z = 2.84). Earlier low-J CO studies of this system found a huge molecular gas reservoir associated with the companion galaxy, while the quasar appeared gas-poor. Our CO observations revealed that the host galaxy of the quasar is also gas-rich, with an estimated molecular gas mass of $\sim (0.7{\!-\!}2.3)\times 10^{10}\, \rm M_{\odot}$. The CO line profiles of the companion galaxy are very broad ($\sim 1000\, \rm km\, s^{-1}$), and show signs of rotation of a compact, massive system. In contrast to previous far-infrared observations, we resolve the continuum emission and detect both sources, with the companion galaxy dominating the dust continuum and the quasar having a $\sim 25{{\ \rm per\ cent}}$ contribution to the total dust emission. By fitting the infrared spectral energy distribution of the sources with mr-moose and empirical templates, the infrared luminosities of the quasar and the companion are in the range of $L_{\rm IR, QSO}\sim (2.1{\!-\!}9.6)\times 10^{12}\, \rm L_{\odot}$ and $L_{\rm IR, Comp.}\sim (2.4{\!-\!}24)\times 10^{12}\, \rm L_{\odot}$, while the estimated star formation rates are $\sim 210{\!-\!}960$ and $\sim 240{\!-\!}2400\, \rm M_{\odot }\, yr^{-1}$, respectively. Our results demonstrate that non-detection of low-J CO transition lines in similar sources does not necessarily imply the absence of massive molecular gas reservoir but that the excitation conditions favour the excitation of high-J transitions.

Smoke on the water: CO and H2O in a circumnuclear disc around a quasar at redshift 2.64

ABSTRACT We present an analysis of observations with the Atacama Large (sub-)Millimetre Array (ALMA) of the 380 GHz water emission line and CO (11–10) emission line from MG J0414+0534, a gravitationally lensed dusty star-forming galaxy that hosts a type 1 quasar. We also present observations at 1.6 GHz with global very long baseline interferometry of the radio source. We confirm the previously reported detection of the 380 GHz water line and that the flux density ratio between the two merging lensed images is reversed with respect to the radio/mm continuum. We further find tentative evidence of variability in the integrated line intensity on time-scales of days. We show that the 380 GHz water line has two components of emission: a disc that is around 35 pc in diameter around the quasar, and another component of emission that is offset ∼600 pc perpendicular to the disc that lies close to the lensing caustic. With lens modelling of the multiwavelength data sets, we construct a model for the quasar system consisting of a circumnuclear disc of molecular gas with a size of about 60 pc bisected by radio jets extending to a distance of about 200 pc from the radio core. Our findings suggest that observations with ALMA of high-excitation molecular lines from strongly lensed quasars could allow detailed studies of active galactic nucleus accretion and feedback at the cosmic peak of black hole and galaxy growth.

High-resolution Near-infrared Polarimetry and Submillimeter Imaging of FS Tau A: Possible Streamers in Misaligned Circumbinary Disk System

Abstract We analyzed the young (2.8 Myr-old) binary system FS Tau A using near-infrared (H-band) high-contrast polarimetry data from Subaru/HiCIAO and submillimeter CO (J = 2–1) line emission data from Atacama Large Millimeter/submillimeter Array (ALMA). Both the near-infrared and submillimeter observations reveal several clear structures extending to ∼240 au from the stars. Based on these observations at different wavelengths, we report the following discoveries. One arm-like structure detected in the near-infrared band initially extends from the south of the binary with a subsequent turn to the northeast, corresponding to two bar-like structures detected in ALMA observations with an local standard of rest kinematic (LSRK) velocity of 1.19–5.64 km s−1. Another feature detected in the near-infrared band extends initially from the north of the binary, relating to an arm-like structure detected in ALMA observations with an LSRK velocity of 8.17–16.43 km s−1. From their shapes and velocities, we suggest that these structures can mostly be explained by two streamers that connect the outer circumbinary disk and the central binary components. These discoveries will be helpful for understanding the evolution of streamers and circumstellar disks in young binary systems.

The Physical Properties of S0 Galaxy PGC 26218: The Origin of Starburst and Star Formation

We present 2D-spectroscopic observations from Centro Astron\'omico Hispano Alem\'an (CAHA) 3.5 m telescope and the millimetre observation from NOrthern Extended Millimeter Array (NOEMA) of the nearby S0 galaxy PGC 26218, which shows central star-formation activity and post-starburst outside in the disk. We estimate the star formation rate (SFR = $0.28\pm0.01$ $M_{\odot} \rm yr^{-1}$) and molecular gas mass ($\rm log\ $$M_{\rm H_{2}}=7.60\pm0.15\ M_{\odot}$) of PGC 26218 based on the extinction-corrected H$\alpha$ emission line and the CO-$\rm H_{2}$ conversion factor ($\alpha_{\rm CO}$) of the Milky Way, respectively. We find that PGC 26218 follows the star forming main sequence (SFMS) and the Kennicutt-Schmidt law. Comparing the kinematics of CO($J$=1-0), stars and H$\alpha$, we find that the rotational axis of CO($J$=1-0) is 45$^{\circ}$ different from that of H$\alpha$. In addition, the profile of the CO($J$=1-0) emission line shows asymmetry and has an inflow component of $\sim$ 46 $\rm km\ s^{-1}$. With the decomposition of the optical image, we confirm that PGC 26218 shows multiple nuclear structures. The projected offset between the most luminous optical center and the center of CO($J$=1-0) is $5.2\arcsec$ ($\sim$ 0.6 kpc) and the latter overlaps with one of the optical cores. These results support that PGC 26218 may have experienced a gas-rich minor merger, extending its star formation and locating it in the SFMS.

C i](1–0) and [C i](2–1) in Resolved Local Galaxies*

Abstract We present resolved [C i] line intensities of 18 nearby galaxies observed with the SPIRE FTS spectrometer on the Herschel Space Observatory. We use these data along with resolved CO line intensities from J up = 1 to 7 to interpret what phase of the interstellar medium the [C i] lines trace within typical local galaxies. A tight, linear relation is found between the intensities of the CO(4–3) and [C i](2–1) lines; we hypothesize this is due to the similar upper level temperature of these two lines. We modeled the [C i] and CO line emission using large-velocity gradient models combined with an empirical template. According to this modeling, the [C i](1–0) line is clearly dominated by the low-excitation component. We determine [C i] to molecular mass conversion factors for both the [C i](1–0) and [C i](2–1) lines, with mean values of α [C i](1−0) = 7.3 M ⊙ K−1 km−1 s pc−2 and α [C i](2−1) = 34 M ⊙ K−1 km−1 s pc−2 with logarithmic root-mean-square spreads of 0.20 and 0.32 dex, respectively. The similar spread of to (derived using the CO(2–1) line) suggests that [C i](1–0) may be just as good a tracer of cold molecular gas as CO(2–1) in galaxies of this type. On the other hand, the wider spread of α [C i](2−1) and the tight relation found between [C i](2–1) and CO(4–3) suggest that much of the [C i](2–1) emission may originate in warmer molecular gas.

ALMA Reveals a Gas-rich, Maximum Starburst in the Hyperluminous, Dust-obscured Quasar W0533–3401 at z ∼ 2.9

Abstract We present ALMA observations and multiwavelength spectral energy distribution analysis in a Wide-field Infrared Survey Explorer-selected, hyperluminous dust-obscured quasar W0533−3401 at z = 2.9. We derive the physical properties of each of its components, such as molecular gas, stars, dust, and the central supermassive black hole (SMBH). Both the dust continuum at 3 mm and the CO line are detected. The derived molecular gas mass M gas = 8.4 × 1010 M ⊙ and its fraction f gas = 0.7 suggest that W0533−3401 is gas-rich. The star formation rate (SFR) has been estimated to be ∼3000–7000 M ⊙ yr−1 by using different methods. The high values of SFR and specific SFR suggest that W0533−3401 is a maximum starburst. The corresponding gas depletion timescales are very short (t depl ∼ 12–28 Myr). The CO emission line is marginally resolved and has a velocity gradient, which is possibly due to a rotating gas disk, gas outflow, or merger. Finally, we infer the black hole mass growth rate of W0533−3401 ( M ⊙ yr−1), which suggests a rapid growth of the central SMBH. The observed black hole to stellar mass ratio M BH/M ⋆ of W0533−3401, which is dependent on the adopted Eddington ratio, is over one order of magnitude higher than the local value, and is evolving toward the evolutionary trend of unobscured quasars. Our results are consistent with the scenario that W0533−3401, with both a gas-rich maximum starburst and a rapid black hole growth, is experiencing a short transition phase toward an unobscured quasar.

ALMA captures feeding and feedback from the active galactic nucleus in NGC 613

We report ALMA observations of CO(3–2) emission in the Seyfert/nuclear starburst galaxy NGC 613, at a spatial resolution of 17 pc, as part of our NUclei of GAlaxies (NUGA) sample. Our aim is to investigate the morphology and dynamics of the gas inside the central kiloparsec, and to probe nuclear fueling and feedback phenomena. The morphology of CO(3–2) line emission reveals a two-arm trailing nuclear spiral at r ≲ 100 pc and a circumnuclear ring at a radius of ∼350 pc that is coincident with the star-forming ring seen in the optical images. Also, we find evidence for a filamentary structure connecting the ring and the nuclear spiral. The ring reveals two breaks into two winding spiral arms corresponding to the dust lanes in the optical images. The molecular gas in the galaxy disk is in a remarkably regular rotation, however the kinematics in the nuclear region are very skewed. The nuclear spectrum of CO and dense gas tracers HCN(4–3), HCO+(4–3), and CS(7–6) show broad wings up to ±300 km s−1, associated with a molecular outflow emanating from the nucleus (r ∼ 25 pc). We derive a molecular outflow mass Mout = 2 × 106 M⊙ and a mass outflow rate of Ṁout = 27 M⊙ yr−1. The molecular outflow energetics exceed the values predicted by AGN feedback models: the kinetic power of the outflow corresponds to PK, out = 20%LAGN and the momentum rate is Ṁoutv ∼ 400LAGN/c. The outflow is mainly boosted by the AGN through entrainment by the radio jet, but given the weak nuclear activity of NGC 613, we might be witnessing a fossil outflow resulting from a previously strong AGN that has now faded. Furthermore, the nuclear trailing spiral observed in CO emission is inside the inner Lindblad resonance ring of the bar. We compute the gravitational torques exerted in the gas to estimate the efficiency of the angular momentum exchange. The gravity torques are negative from 25 to 100 pc and the gas loses its angular momentum in a rotation period, providing evidence for a highly efficient inflow towards the center. This phenomenon shows that the massive central black hole has significant dynamical influence on the gas, triggering the inflowing of molecular gas to feed the black hole.

Anomalously Narrow Line Widths of Compact Massive Star-forming Galaxies at z ∼ 2.3: A Possible Inclination Bias in the Size–Mass Plane

Abstract Compact, massive star-forming galaxies at z ∼ 2.5 are thought to be building the central regions of giant elliptical galaxies today. However, a significant fraction of these objects were previously shown to have much smaller Hα line widths than expected. A possible interpretation is that Hα emission from their central regions, where the highest velocities are expected, is typically obscured by dust. Here we present Atacama Large Millimeter/submillimeter Array observations of the CO(3–2) emission line of three compact, massive galaxies with Hα line widths of FWHM(Hα) ∼ 125–260 km s−1 to test this hypothesis. Surprisingly, in all three galaxies, the CO line width is similar to the Hα line width: we find FWHM(CO) ∼ 165 km s−1 for all three galaxies whereas FWHM(CO) ∼ 450–700 km s−1 was expected from a simple virial estimator. These results show that the narrow Hα line widths of many compact massive star-forming galaxies are not due to preferential obscuration of the highest velocity gas. An alternative explanation for the narrow line widths is that the galaxies are disks that are viewed nearly face-on. We suggest that there may be an inclination bias in the size–mass plane, such that the apparent rest-frame optical sizes of face-on galaxies are smaller than those of edge-on galaxies. Although not conclusive, this hypothesis is supported by an observed anti-correlation between size and axis ratio of massive galaxies.

Flybys in protoplanetary discs – II. Observational signatures

ABSTRACT Tidal encounters in star clusters perturb discs around young protostars. In Cuello et al., we detailed the dynamical signatures of a stellar flyby in both gas and dust. Flybys produce warped discs, spirals with evolving pitch angles, increasing accretion rates, and disc truncation. Here, we present the corresponding observational signatures of these features in optical/near-infrared scattered light and (sub) millimetre continuum and CO line emission. Using representative prograde and retrograde encounters for direct comparison, we post-process hydrodynamical simulations with radiative transfer methods to generate a catalogue of multiwavelength observations. This provides a reference to identify flybys in recent near-infrared and submillimetre observations (e.g. RW Aur, AS 205, HV Tau and DO Tau, FU Ori, V2775 Ori, and Z CMa).

Gas shells and magnetic fields in the Orion-Eridanus superbubble

Aims. The Orion-Eridanus superbubble has been blown by supernovae and supersonic winds of the massive stars in the Orion OB associations. It is the nearest site at which stellar feedback on the interstellar medium that surrounds young massive clusters can be studied. The formation history and current structure of the superbubble are still poorly understood, however. It has been pointed out that the picture of a single expanding object should be replaced by a combination of nested shells that are superimposed along the line of sight. We have investigated the composite structure of the Eridanus side of the superbubble in the light of a new decomposition of the atomic and molecular gas. Methods. We used H I 21 cm and CO (J = 1−0) emission lines to separate coherent gas shells in space and velocity, and we studied their relation to the warm ionised gas probed in Hα emission, the hot plasma emitting X-rays, and the magnetic fields traced by dust polarised emission. We also constrained the relative distances to the clouds using dust reddening maps and X-ray absorption. We applied the Davis–Chandrasekhar–Fermi method to the dust polarisation data to estimate the plane-of-sky components of the magnetic field in several clouds and along the outer rim of the superbubble. Results. Our gas decomposition has revealed several shells inside the superbubble that span distances from about 150–250 pc. One of these shells forms a nearly complete ring filled with hot plasma. Other shells likely correspond to the layers of swept-up gas that is compressed behind the expanding outer shock wave. We used the gas and magnetic field data downstream of the shock to derive the shock expansion velocity, which is close to ~20 km s−1. Taking the X-ray absorption by the gas into account, we find that the hot plasma inside the superbubble is over-pressured compared to plasma in the Local Bubble. The plasma comprises a mix of hotter and cooler gas along the lines of sight, with temperatures of (3–9) and (0.3 − 1.2) × 106 K, respectively. The magnetic field along the western and southern rims and in the approaching wall of the superbubble appears to be shaped and compressed by the ongoing expansion. We find plane-of-sky magnetic field strengths from 3 to 15 μG along the rim.

Quantifying the thermal Sunyaev–Zel’dovich effect and excess millimetre emission in quasar environments

ABSTRACT In this paper, we probe the hot, post-shock gas component of quasar-driven winds through the thermal Sunyaev–Zel’dovich (tSZ) effect. Combining data sets from the Atacama Cosmology Telescope, the Herschel Space Observatory, and the Very Large Array, we measure average spectral energy distributions of 109 829 optically selected, radio quiet quasars from 1.4 to 3000 GHz in six redshift bins between 0.3 < z < 3.5. We model the emission components in the radio and far-infrared, plus a spectral distortion from the tSZ effect. At z > 1.91, we measure the tSZ effect at 3.8σ significance with an amplitude corresponding to a total thermal energy of 3.1 × 1060 erg. If this energy is due to virialized gas, then our measurement implies quasar host halo masses are ∼6 × 1012 h−1 M⊙. Alternatively, if the host dark matter halo masses are ∼2 × 1012 h−1 M⊙ as some measurements suggest, then we measure a >90 per cent excess in the thermal energy over that expected due to virialization. If the measured SZ effect is primarily due to hot bubbles from quasar-driven winds, we find that $(5^{+1.2}_{-1.3}$) per cent of the quasar bolometric luminosity couples to the intergalactic medium over a fiducial quasar lifetime of 100 Myr. An additional source of tSZ may be correlated structure, and further work is required to separate the contributions. At z ≤ 1.91, we detect emission at 95 and 148 GHz that is in excess of thermal dust and optically thin synchrotron emission. We investigate potential sources of this excess emission, finding that CO line emission and an additional optically thick synchrotron component are the most viable candidates.