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Register a new userLuminous, pc-scale CO 6-5 emission in the obscured nucleus of NGC1377
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High resolution submm observations are important in probing the morphology, column density and dynamics of obscured active galactic nuclei (AGNs). With high resolution (0.06 x 0.05) ALMA 690 GHz observations we have found bright (TB >80 K) and compact (FWHM 10x7 pc) CO 6-5 line emission in the nucleus of the extremely radio-quiet galaxy NGC1377. The integrated CO 6-5 intensity is aligned with the previously discovered jet/outflow of NGC1377 and is tracing the dense (n>1e4 cm-3), hot gas at the base of the outflow. The velocity structure is complex and shifts across the jet/outflow are discussed in terms of jet-rotation or separate, overlapping kinematical components. High velocity gas (deltaV +-145 km/s) is detected inside r<2-3 pc and we suggest that it is emerging from an inclined rotating disk or torus of position angle PA=140+-20 deg with a dynamical mass of approx 3e6 Msun. This mass is consistent with that of a supermassive black hole (SMBH), as inferred from the M-sigma relation. The gas mass of the proposed disk/torus constitutes <3% of the nuclear dynamical mass. In contrast to the intense CO 6-5 line emission, we do not detect dust continuum with an upper limit of S(690GHz)<2mJy. The corresponding, 5 pc, H2 column density is estimated to N(H2)<3e23 cm-2, which is inconsistent with a Compton Thick (CT) source. We discuss the possibility that CT obscuration may be occuring on small (subparsec) or larger scales. From SED fitting we suggest that half of the IR emission of NGC1377 is nuclear and the rest (mostly the far-infrared (FIR)) is more extended. The extreme radio quietness, and the lack of emission from other star formation tracers, raise questions on the origin of the FIR emission. We discuss the possibility that it is arising from the dissipation of shocks in the molecular jet/outflow or from irradiation by the nuclear source along the poles.
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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.
Young massive stars regulate the physical conditions, ionization, and fate of their natal molecular cloud. It is important to find tracers that help quantifying the stellar feedback processes that take place at different scales. We present ~85 arcmin^2 velocity-resolved maps of several submm molecular lines toward the closest high-mass star-forming region, OMC-1. The observed rotational lines include probes of warm and dense molecular gas that are difficult to detect from ground-based telescopes: CH+ (1-0), CO (10-9), HCO+ (6-5), and HCN (6-5). These lines trace an extended but thin layer of molecular gas at high thermal pressure, P_th ~ 1e7-1e9 K/cm3, associated with the FUV-irradiated surface of OMC-1. The intense FUV field, emerging from massive stars in the Trapezium cluster, heats, compresses and photoevaporates the cloud edge. It also triggers the formation of reactive molecules such as CH+. The CH+ (1-0) emission spatially correlates with the flux of FUV photons impinging the cloud: G_0 from 1e3 to 1e5. This correlation is supported by isobaric PDR models in the parameter space P_th/G_0 ~ [5e3-8e4] K/cm3 where many PDRs seem to lie. The CH+ (1-0) emission correlates with the extended emission from vibrationally excited H2, and with that of [CII]158um and CO 10-9, all emerging from FUV-irradiated gas. These correlations link the presence of CH+ to the availability of C+ ions and of FUV-pumped H2(v>0) molecules. The parsec-scale CH+ emission and narrow-line (dv ~ 3 km/s) mid-J CO emission arises from extended PDRs and not from fast shocks. PDR line tracers are the smoking gun of the stellar feedback from young massive stars. The PDR component in OMC-1 represents 5 to 10% of the total gas mass, however, it dominates the emitted line luminosity. These results provide insights into the source of submm CH+ and mid-J CO emission from distant star-forming galaxies.
With high resolution (0.25 x 0.18) ALMA CO 3-2 observations of the nearby (D=21 Mpc, 1=102 pc), extremely radio-quiet galaxy NGC1377, we have discovered a high-velocity, very collimated nuclear outflow which we interpret as a molecular jet with a projected length of +-150 pc. Along the jet axis we find strong velocity reversals where the projected velocity swings from -150 km/s to +150 km/s. A simple model of a molecular jet precessing around an axis close to the plane of the sky can reproduce the observations. The velocity of the outflowing gas is difficult to constrain due to the velocity reversals but we estimate it to be between 240 and 850 km/s and the jet to precess with a period P=0.3-1.1 Myr. The CO emission is clumpy along the jet and the total molecular mass in the high-velocity (+-(60 to 150 km/s)) gas lies between 2e6 Msun (light jet) and 2e7 Msun (massive jet). There is also CO emission extending along the minor axis of NGC1377. It holds >40% of the flux in NGC1377 and may be a slower, wide-angle molecular outflow which is partially entrained by the molecular jet. We discuss the driving mechanism of the molecular jet and suggest that it is either powered by a very faint radio jet or by an accretion disk-wind similar to those found towards protostars. The nucleus of NGC1377 harbours intense embedded activity and we detect emission from vibrationally excited HCN J=4-3 v_2=1f which is consistent with hot gas and dust. We find large columns of H2 in the centre of NGC1377 which may be a sign of a high rate of recent gas infall. The dynamical age of the molecular jet is short (<1 Myr), which could imply that it is young and consistent with the notion that NGC1377 is caught in a transient phase of its evolution. However, further studies are required to determine the age of the molecular jet, its mass and the role it is playing in the growth of the nucleus of NGC1377.
We present high-quality ALMA Band 8 observations of the [CI] $^3P_1$-$^3P_0$ line and 609 $mu$m dust continuum emission toward the nearby luminous infrared galaxy (LIRG) IRAS F18293-3413, as well as matched resolution (300-pc scale) Band 3 CO $J=$1-0 data, which allow us to assess the use of the [CI] $^3P_1$-$^3P_0$ line as a total gas mass estimator. We find that the [CI] line basically traces structures detected in CO (and dust), and a mean (median) [CI]/CO luminosity ($L_{rm [CI]}$/$L_{rm CO}$) ratio of 0.17 (0.16) with a scatter of 0.04. However, a pixel-by-pixel comparison revealed that there is a radial $L_{rm [CI]}$/$L_{rm CO}$ gradient and a superlinear $L_{rm CO}$ vs. $L_{rm [CI]}$ relation (slope = 1.54 $pm$ 0.02) at this spatial scale, which can be explained by radial excitation and/or line opacity gradients. Based on the molecular gas masses converted from the dust continuum emission, we found that the CO-to-H$_2$ and [CI]-to-H$_2$ conversion factors are relatively flat across the molecular gas disk with a median value of 3.5$^{+1.9}_{-1.3}$ and 20.7$^{+9.2}_{-4.9}$ $M_{odot}$ (K km s$^{-1}$ pc$^2$)$^{-1}$, respectively. A non-LTE calculation yields that typical molecular gas properties seen in nearby (U)LIRGs ($n_{rm H_2}$ = 10$^{3-4}$ cm$^{-3}$, $T_{rm kin}$ $sim$ 50 K, and $X_{rm CI}$ = (0.8-2.3) $times$ 10$^{-5}$) can naturally reproduce the derived [CI]-to-H$_2$ conversion factor. However, we caution that a careful treatment of the physical gas properties is required in order to measure H$_2$ gas mass distributions in galaxies using a single [CI] line. Otherwise, a single [CI] line is not a good molecular gas estimator in a spatially resolved manner.
We present a multiwavelength study of an atypical submillimeter galaxy in the GOODS-North field, with the aim to understand its physical properties of stellar and dust emission, as well as the central AGN activity. Although it is shown that the source is likely an extremely dusty galaxy at high redshift, its exact position of submillimeter emission is unknown. With the new NOEMA interferometric imaging, we confirm that the source is a unique dusty galaxy. It has no obvious counterpart in the optical and even NIR images observed with HST at lambda~<1.4um. Photometric-redshift analyses from both stellar and dust SED suggest it to likely be at z~>4, though a lower redshift at z~>3.1 cannot be fully ruled out (at 90% confidence interval). Explaining its unusual optical-to-NIR properties requires an old stellar population (~0.67 Gyr), coexisting with a very dusty ongoing starburst component. The latter is contributing to the FIR emission, with its rest-frame UV and optical light being largely obscured along our line of sight. If the observed fluxes at the rest-frame optical/NIR wavelengths were mainly contributed by old stars, a total stellar mass of ~3.5x10^11Msun would be obtained. An X-ray spectral analysis suggests that this galaxy harbors a heavily obscured AGN with N_H=3.3x10^23 cm^-2 and an intrinsic 2-10 keV luminosity of L_X~2.6x10^44 erg/s, which places this object among distant type 2 quasars. The radio emission of the source is extremely bright, which is an order of magnitude higher than the star-formation-powered emission, making it one of the most distant radio-luminous dusty galaxies. The combined characteristics of the galaxy suggest that the source appears to have been caught in a rare but critical transition stage in the evolution of submillimeter galaxies, where we are witnessing the birth of a young AGN and possibly the earliest stage of its jet formation and feedback.
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