Chemistry in luminous AGN and starburst galaxies

Molecular line emission is a useful tool for probing the highly obscured inner kpc of starburst galaxies and buried AGNs. Molecular line ratios serve as diagnostic tools of the physical conditions of the gas—but also of its chemical properties. Both provide important clues to the type and evolutionary stage of the nuclear activity. While CO emission remains the main tracer for molecular distribution and dynamics, molecules such as HCN, HNC, HCO⁺, CN and HC₃N are useful for probing the properties of the denser (n≳10⁴ cm⁻³), star-forming gas. Here I discuss current views on how line emission from these species can be interpreted in luminous galaxies. HNC, HCO⁺ and CN are all species that can be associated both with photon dominated regions (PDRs) in starbursts—as well as X-ray dominated regions (XDRs) associated with AGN activity. HC₃N line emission may identify galaxies where the starburst is in the early stage of its evolution.     

Molecular Gas in the Merging System ARP 299

We present new observations of the molecular gas distribution in the merging system Arp 299. The first observation set was obtained with the Canada–France–Hawaii Telescope near-IR camera Redeye and the second set comes from the IRAM Plateau de Bure interferometer (combined with short spacings observed at the IRAM 30 m Telescope). In the near IR, H₂ ν=1→0 S(1) and Br_γ line maps are globally identical: there is bright emission not only at the two galaxy nuclei but also in numerous extranuclear star forming regions. Moreover, there is weaker emission localized in filaments between and around the two nuclei. These filaments correspond to a dust lane observed in optical images from HST. ¹²CO(1→0), ¹³CO(1→0) and HCN(1→0) maps are also presented. The structure of the¹²CO(1→0) map is very close to the NIR observations: the same bright galaxy nuclei and star-forming regions, the same filaments, but half of the total flux is found in weak extended emission. Strong HCN emission is observed in the nucleus A indicating the presence of a large amount of dense gas. Nucleus B1 is weak in ¹²CO(1→0) emission while nucleus A and star-forming regions C-C′ show more normal ¹³CO/¹²CO ratios. This revised version was published online in July 2006 with corrections to the Cover Date.     

A new evolutionary scenario of intermediate-mass star-formation revealed by multi-wavelength observations of OMC-2/3

We have performed millimeter- and submilli- meter-wave survey observations using the Nobeyama millimeter array (NMA) and the Atacama Submillimeter Telescope Experiment (ASTE) in one of the nearest intermediate-mass (IM) star-forming regions: Orion Molecular Cloud-2/3 (OMC-2/3). Using the high-resolution capabilities offered by the NMA (∼several arcsec), we observed dust continuum and H¹³CO⁺(1–0) emission in 12 pre- and proto-stellar candidates identified previously in single-dish millimeter observations. We unveiled the evolutionary changes with variations of the morphology and velocity structure of the dense envelopes traced by the H¹³CO⁺(1–0) emission. Furthermore, using the high-sensitivity capabilities offered by the ASTE, we searched for large-scale molecular outflows associated with these pre- and proto-stellar candidates observed with the NMA. As a result of the CO(3–2) observations, we detected six molecular outflows associated with the dense gas envelopes traced by H¹³CO⁺(1–0) and 3.3 mm continuum emission. The estimated CO outflow momentum increases with the evolutionary sequence from early to late type of the protostellar cores. We also found that the 24 μm flux increases as the dense gas evolutionary sequence. We propose that the enhancement of the 24 μm flux is caused by the growth of the cavity (i.e. the CO outflow destroys the envelope) as the evolutionary sequence. Our results show that the dissipation of the dense gas envelope plays an essential role in the evolution of the IM protostars. The extremely high-sensitivity and high-angular resolution offered by ALMA will reveal unprecedented details of the inner ∼50 AU of these protostars, which will provide us a break through in the classic scenario of IM star/disk formation.     

亮红外星系NGC 1614中多谱线示踪的致密分子气体

利用高空间分辨率的¹²CO(1-0)、¹³CO(1-0)、¹²CO(3-2)、¹²CO(6-5)、HCN(3-2)、\lk HCN(4-3)、 HCO⁺(3-2)和HCO⁺(4-3)分子谱线的ALMA (Atacama Large Millimeter/ submillimeter Array)归档数据, 来研究近邻亮红外星系NGC 1614的分子气体性质, 尤其是致密分子气体的性质. 在高分辨率分子气体谱线的积分强度图中, 在星系中心区域($<$ 1kpc)可以看到环状结构, 分子气体主要分布于星系中心区域, 核区分子气体含量较少. ¹²CO(1-0)显示出向南部、 北部以及东南部的延展结构, 高阶的CO ($J \ge$ 3, J为转振能级量子数)分子谱线和致密分子HCN、HCO⁺谱线显示, 较致密的分子气体主要集中于星系中心区域. HCN(4-3)/¹²CO(1-0)和HCN⁺(4-3)/¹²CO(1-0)积分强度比值图显示, 致密分子气体主要集中于中心区域的环状结构上. HCN/HCO⁺强度比值的分布变化表明星暴环的不同区域可能具有不同的激发条件. HCN/HCO⁺(4-3)强度比值分布在环的东、西部(sim0.44 pm 0.04)高于环的南、北部(sim0.35 pm 0.03). HCN/HCO⁺(3-2)强度比值较高的区域(sim0.38 pm 0.04)分布在HCN(3-2)峰值位置, 而环的西北、东南部强度比值相对较低(sim0.3 pm 0.03). 对于中心不同区域 HCN/HCO⁺比值变化的原因进行了讨论.     

Dense Gas, Chemistry and Star Formation in Luminous Galaxies

The molecular phase of the ISM constitutes the main source of fuel for the activity in starburst and AGNs. The physical conditions and chemical constitution of the molecular gas will change with, and respond to, the evolution of the activity. This paper includes a short discussion of the ¹²CO/¹³CO 1–0 line intensity ratio as a diagnostic tool of the molecular gas properties of luminous galaxies – paired with examples of high-resolution studies of how the line ratio varies within galaxies. A possible connection between the OH megamasers and galaxies with unusually high ¹²CO/¹³CO 1–0 line intensity ratios are also briefly discussed.The relative intensities of the dense gas tracers HNC, HCN, HCO⁺ and CN are a result of both chemistry and starburst evolution. The discussion on the interpretation of HNC 1–0 emission includes the importance of ion-neutral chemistry in a luminous starburst region. Finally, simple cartoon ISM models and how they can be applied to LIRGs and ULIRGs, are presented.     

Dense molecular gas in a sample of LIRGs and ULIRGs: The low-redshift connection to the huge high-redshift starbursts and AGNs

The sample of nearby LIRGs and ULIRGs for which dense molecular gas tracers have been measured is building up, allowing for the study of the physical and chemical properties of the gas in the variety of objects in which the most intense star formation and/or AGN activity in the local universe is taking place. This characterisation is essential to understand the processes involved, discard others and help to interpret the powerful starbursts and AGNs at high redshift that are currently being discovered and that will routinely be mapped by ALMA. We have studied the properties of the dense molecular gas in a sample of 17 nearby LIRGs and ULIRGs through millimeter observations of several molecules (HCO⁺, HCN, CN, HNC and CS) that trace different physical and chemical conditions of the dense gas in these extreme objects. In this paper we present the results of our HCO⁺ and HCN observations. We conclude that the very large range of measured line luminosity ratios for these two molecules severely questions the use of a unique molecular tracer to derive the dense gas mass in these galaxies.     

基于ALMA高分辨率的多谱线数据对 NGC 1068核区中物理性质的研究

利用ALMA干涉阵望远镜(Atacama Large Millimeter/submillimeter Array)的高分辨(～0.2′′–0.7′′)的多谱线数据,包括CO (1-0)、CO (2-1)、CO (3-2)、HCN (1-0)、HCO⁺(1-0)、 HCN (3-2)、 HCO⁺(3-2)、HCN (4-3)和HCO+(4-3),并结合连续谱数据对近邻星系NGC 1068核区的物理性质进行了研究.速度积分强度图显示核周盘(CircumNuclear Disk, CND)呈现不对称的环状结构,尺度～300 pc.各分子谱线均显示, CND上的东发射结(E-knot)比西发射结(W-knot)有着更强的发射,且E-knot处表现出的分子气体的速度比W-knot更高.致密分子气体含量占比(用HCN或HCO⁺不同转动跃迁线与CO (1-0)的积分强度比值表示),以及致密分子气体比值(HCN/HCO⁺)均在CND的东部表现出更高的值,意味着CND东部和西部有着不同的物理环境或化学组成. CO ...     

12CO, 13CO and HCN in the Barred Galaxy NGC 1530

Bars probably have a great importance in galactic evolution. The barred potential is able to concentrate large quantities of interstellar gas in the vicinity of the nucleus, feeding any nuclear activity, be it central starbursts or black hole accretion discs. The IRAM millimeter interferometer and 30 m telescope have allowed a precise analysis of the molecular gas in the bar and the nucleus of a typical barred spiral galaxy, NGC 1530. In this galaxy, I have detected CO(1→0) along two lanes that trace shocks in the molecular gas. In these lanes, the gas moves toward the centre of the galaxy, with typical in fall velocities of 100 km s^-1. I have shown in these shocks an anticorrelation between shear in the gas and star formation efficiency by comparing H^α and CO maps. I have also studied the centre of this galaxy at higher resolution in¹²CO(1→0), ¹²CO(2→1),¹³CO(1→0) and HCN(1→0). In the central region, the gas distribution is a ring or an unresolved spiral, surrounded by two curved arcs. The nuclear ring contains large amounts of dense gas traced by HCN and ¹³CO, and shows intense star formation, as indicated by the non-thermal centimetre continuum. The arcs, in contrast, are poor in dense gas and form few stars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Probing the feeding and feedback of activity near and far

High-resolution CO maps are an essential tool to search for observational evidence of AGN fueling in galaxy nuclei. While their capabilities will be surpassed by ALMA, current mm-interferometers can already provide relevant information on scales which are critical for the process of angular momentum transfer in fueling the AGN. In this context we present the latest results issued from the NUclei of GAlaxies (NUGA) project, a high-resolution (0.5^′′–1^′′) CO survey of low luminosity AGNs conducted with the IRAM Plateau de Bure interferometer (PdBI). The use of more specific molecular tracers of dense gas can probe the feedback influence of activity on the chemistry and energy balance in the interstellar medium of nearby galaxies, a prerequisite to understanding how feedback operate at higher redshift galaxies. We discuss the results obtained in an ongoing study devoted to probe the feedback of activity from nearby Seyferts to high-redshift QSO.     

Methods and Results of an Optical Search for Extraterrestrial Civilizations

I summarize fully-sampled observations of the 3 mm emission from CO and HCN in the inner arcminute of NGC 1068. The CO emission is distributed in the form of a molecular bar, coincident with the infrared bar, from which emanate two spiral arms. A relatively weak concentration of CO line emission is found at the nucleus. By contrast, the HCN emission is strongly concentrated at the center, with relatively weak emission in the region of the star-forming arms. The ratio of HCN to CO integrated intensities is about 0.6 over the central r ≉ 175 pc and is the highest ratio measured in the center of any galaxy; the ratio reflects the high thermal pressure (TK ~ 50 K, n[H2] ~ 4 × 106 cm-3) in the few hundred parsecs surrounding the nucleus. The kinematics in the star-forming arms are well described by circular orbits, with ordered noncircular motions of < 30 km s-1 that may be attributed to spiral density wave streaming. Interior to the bar, noncircular motions dominate the gas kinematics. A model of the CO kinematics contrains any Inner Lindblad Resonance to be close to the location of the hundred-parsec scale HCN ‘disk’. At the nucleus, the spatially unresolved CO emission shows a triplet velocity structure characteristic of kinematically independent regions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Searching for X-Ray Luminous Starburst Galaxies

The existence or otherwise of X-ray luminous star-forming galaxies has been an open question since the era of the Einstein satellite. Various authors have claimed the discovery of X-ray luminous star-forming galaxies but in many cases more careful spectroscopic studies of these objects have shown that many of them are in fact obscured AGN. In order to investigate the possibility that such a class of galaxies do exist, we have carried out a cross-correlation between optical and IRAS samples of galaxies which are known to contain large numbers of star-forming galaxies and catalogues of sources detected in X-ray surveys. The selection criteria for the optical follow-up observations was based on their X-ray and infrared (IRAS) colours and their X-ray luminosities. We note that this sample is by no means complete or uniformly selected and hence cannot be used for statistical studies; nevertheless, confirmation of the existence of such a class of objects would be an important step and would require us to understand the physical process responsible for such powerful X-ray emission. We have initiated an optical spectroscopic survey in order to obtain accurate spectroscopic classifications for all the objects which are claimed to be starburst galaxies. Here we present preliminary results from this survey. We have discovered a number of starburst galaxies with X-ray luminosities above ～ 10⁴¹ erg s^-1 (for H ₀=50 km s^-1 Mpc^-1).We investigate possible origins for the X-ray emission in individual cases.     

Tidal dwarf galaxies in the Stephan's Quintet?

We present kinematics and photometric evidence for the presence of seven candidate tidal dwarf galaxies in Stephan's Quintet. The central regions of the two most probable parent galaxies, NGC 7319 and NGC 7318B, contain little or no gas whereas the intragroup medium and, in particular, the optical tails that seem to be associated with NGC 7318B are rich in cold and ionized gas. Two tidal dwarf candidates may be located at the edge of a tidal tail, another located within a tail, and for the four others there is no obvious stellar/gaseous bridge between them and the parent galaxy. Two of the candidates are associated with H I clouds, one of which is, in addition, associated with a CO cloud. All seven regions have low continuum fluxes and high Hα luminosity densities [F(Hα) = (1-60) × 10-14 ergs s^-1 cm^-2]. Their magnitudes (M_B = –16.1 to –12.6), sizes (∼ 3.5 h₇₅ ^-1 kpc), colors (typically B – R = 0.7), and gas velocity gradients (∼ 8 –26 h₇₅ km s^-1 kpc^-1) are typical for tidal dwarf galaxies. In addition, the ratios between their star formation rates determined from Hα and from the B-band luminosity are typical of other tidal dwarf galaxies. The masses of the tidal dwarf galaxies in Stephan's Quintet range from ∼ 2 × 10⁸ to 10¹⁰ M_⊙, and the median value for their inferred mass-to-light ratios is 7 (M/L)_⊙. At least two of the systems may survive possible ‘fallbacks’ or disruption by the parent galaxies and may already be, or turn into, self-gravitating dwarf galaxies, new members of the group. This revised version was published online in September 2006 with corrections to the Cover Date.     

The BIMA Survey of Nearby Galaxies (BIMA SONG)

BIMA SONG is a systematic imaging study of the 3 mm CO J = 1 → 0molecular emission within the centres and discs of 44 nearby spiral galaxies on size scales of a few hundred parsecs (6-9"). The overall goal of the survey is to study the role of molecular gas in the evolution of spiral galaxies. To this end, BIMA SONG addresses 1) the distribution and physical conditions of the molecular gas in galactic discs and its relation to star formation, 2) the effects of a stellar bar on the kinematics of molecular gas, including the possible inflow of gas along a bar, and 3) the distribution and role of molecular gas in the central few hundred parsecs of active and quiescent galaxies. The source list includes all (except M33and M31) 44 galaxies of Hubble types Sa–Sd, with declinations δ >−20^°, visual magnitudes B < 11.0, velocities v _hel <2000 km s^-1, and inclinations i < 70^°. Beyond the specific scientific questions we will address, this survey will provide a unique database for astronomers who study galaxies at all wavelengths. This revised version was published online in July 2006 with corrections to the Cover Date.     

ASTE observations of the massive-star forming region Sgr B2: a giant impact scenario

We report mapping observations of a 35 pc × 35 pc region covering the Sgr B2 molecular cloud complex in the ¹³CO (3-2) and the CS (7-6) lines using the ASTE 10 m telescope with high angular resolution. The central region was mapped also in the C¹⁸O (3-2) line. The images not only reproduce the characteristic structures noted in the preceding millimeter observations, but also highlight the interface of the molecular clouds with a large velocity jump of a few tens of km s⁻¹. These new results further support the scenario that a cloud–cloud collision has triggered the formation of massive cloud cores, which form massive stars of Sgr B2. Prospects of exciting science enabled by ALMA are discussed in relation to these observations.     

Maps of hco+ Emission in c/1995 o1 (Hale–Bopp)

On-the-Fly maps of emission from the HCO⁺ J = 3-2 transition at 267.6 GHz were obtained of C/1995 O1 (Hale-Bopp) on 1997 Mar 15.6 UT using the NRAO 12-m telescope with high spatial resolution. Unlike the relatively symmetric and centralized maps of the neutral species CO, HCN and H₂CO, the spatial extent of HCO⁺ emission is very diffuse with a complex structure characterized by at least two physically different regions. The bulk of the HCO⁺ emission peaks in intensity ∼175,000 km anti-sunward from the nuclear position. This peak emission does not fall directly along the anti-sunward direction, but is rotated by ∼10 degrees toward the east from the anti-sunward direction. A substantial void, or decrease, of HCO⁺ emission is observed within ∼ 55,000 km of the nucleus. The HCO⁺ emission in this void is roughly half the intensity of the emission observed 100,000 km away. This decrease of HCO⁺ emission near the nucleus may indicate that production or excitation of HCO⁺ is inhibited, or perhaps that HCO⁺ is easily destroyed in the inner coma, especially within ∼50,000 km of the nucleus. This void roughly coincides with the approximate location and size of the so-called “diamagnetic cavity” in the coma and may mark a significant transition region in the inner coma of Hale-Bopp This revised version was published online in July 2006 with corrections to the Cover Date.     

The Evolution of Star-Forming Galaxies: The SFR Density of the Universe

The evolution of the Star Formation Rate (SFR) density of the Universe as a function of look-back time is a fundamental parameter in order to understand the formation and evolution of galaxies. The current picture, only outlined in the last years, is that the global SFR density has dropped by about an order of magnitude from a redshift of z∼1.5 to the current value at z=0. Because these SFR density studies are now extended to the whole range in redshift, it becomes mandatory to combine data from different SFR tracers. At low redshifts, optical emission lines are the most widely used. Using Hα as current-SFR tracer, the Universidad Complutense de Madrid (UCM) Survey provided the first estimation of the global SFR density in the Local Universe. The Hα flux in emission is directly related to the number of ionizing photons and, modulo IMF, to the total mass of stars formed. Metallic lines like [OII]λ3727 and [OIII]λ5007 are affected by metallicity and excitation. Beyond redshifts z∼0.4, Hα is not observable in the optical and [OII]λ3727 or UV luminosities have to be used. The UCM galaxy sample has been used to obtain a calibration between [OII]λ3727 luminosity and SFR specially suitable for the different types of star-forming galaxies found by deep spectroscopic surveys in redshifts up to z∼1.5. These calibrations, when applied to recent deep redshift surveys confirm the drop of the SFR density of the Universe since z∼1 previously infered in the UV. However, the fundamental parameter that determines galactic evolution is mass, not luminosity. The mass function for local star-forming galaxies is critical for any future comparison with other galaxy populations of different evolutionary status. Hα velocity-widths for UCM galaxies indicate that besides a small fraction of 10¹⁰-10¹¹ M_⊙ starburst nuclei spirals, the majority have dynamical masses in the ∼10⁹ M_⊙ range. A comparison with published data for faint blue galaxies suggests that star-forming galaxies at z∼1 would have SFR per unit mass and burst strengths similar to those at z=0, but being intrinsically more massive. This revised version was published online in July 2006 with corrections to the Cover Date.     

The CO to H2 Conversion Factor in Normal Late-Type Galaxies

The molecular gas mass in nearby galaxies is generally estimated using ¹²CO(1-0) line intensities and assuming the X conversion factor between I(CO) and N(H₂) measured in the solar neighborhood. It is however known that this X conversion factor is not universal since it changes with metallicity, cosmic ray density and UV radiation field. Far-IR data in the spectral range 100-1000 μm can be used to estimate the molecular gas content of late-type galaxies in an independent way of CO line measurements once a metallicity-dependent dust to gas ratio is assumed, allowing a direct estimate of X. This exercise is presented here for a large sample of galaxies with available multifrequency data. X spans from ∼ 10²⁰ mol cm^-2 (K km s^-1)^-1 in giant spirals to ∼ 10²¹ mol cm^-2 (K km s^-1)^-1 in dwarf irregulars. This revised version was published online in September 2006 with corrections to the Cover Date.     

Normal galaxies in the all-sky survey by the eROSITA X-ray telescope of the Spectrum-X-Gamma observatory

We analyze the statistical properties of normal galaxies to be detected in the all-sky survey by the eROSITA X-ray telescope of the Spectrum-X-Gamma observatory. With the current configuration and parameters of the eROSITA telescope, the sensitivity of a 4-year-long all-sky survey will be ≈10^?14 erg s^?1 in the 0.5–2 keV band. This will allow ～(1.5–2) × 10⁴ normal galaxies with approximately the same contribution of star-forming and elliptical galaxies to be detected. All galaxies of the X-ray survey are expected to enter into the existing far-infrared (IRAS) or near-infrared (2MASS) catalogs; the sample of star-forming galaxies will be approximately equivalent in sensitivity to the sample of star-forming galaxies in the IRAS catalog of infrared sources. Thus, a large homogeneous sample of normal galaxies with measured X-ray, near-infrared, and far-infrared fluxes will be formed. About 90% of the galaxies in the survey are located within ～200–400 Mpc. A typical (most probable) galaxy will have a luminosity log L _X ～ 40.5–41.0, will be located at a distance of ～70–90 Mpc, and will be either a star-forming galaxy with a star formation rate of ～20M _⊙ yr^?1 whose X-ray emission is produced by ultraluminous X-ray sources (ULXs) or an elliptical galaxy with amass log M _* ～ 11.3 emitting through to a hot interstellar gas. The galaxies within 35 Mpc will collectively contain ～10² ULXs with luminosities log L _X > 40, ～80% of whichwill be the only luminous source in the galaxy. Thus, although the angular resolution of the eROSITA telescope is too low for the luminosity function of compact sources in galaxies to be studied in detail, the survey data will allow one to investigate its bright end and, possibly, to impose constraints on the maximum luminosity of ULXs.     

Flattening of galaxies of different morphological types in subclusters of Coma

This paper deals with the observed variation in the flattening of galaxies with the density of galaxies in the subclusters of Coma surrounding NGC 4889, NGC 4874, and NGC 4839 based on data from the Abastumani Combined Catalog of Galaxies. The mean values of the observed ratios of the diameters of the galaxies, as well as histograms of their distributions, indicate that in the central, dense regions of the subclusters within a volume of 0.5h ₇₅ ⁻¹ Mpc³, E and S0 type galaxies are close to spheroidal. A significant reduction in the mean values of the diameters of the galaxies in the subclusters is noted, regardless of their morphology relative to the galaxies in the halo of the Coma cluster. In the subclusters, spiral galaxies are found with a hydrogen deficit that is more than 5 times the hydrogen deficit in spirals within the halo of the cluster. According to their 3-D coordinates, most of the galaxies with a hydrogen deficit are located closer to the south-east edge of the subcluster surrounding NGC 4874 near an extended gas filament in the x-ray region. This may indicate that the subcluster is moving toward a central condensation of faint galaxies in the Coma cluster and a possible merger with it. __________ Translated from Astrofizika, Vol. 50, No. 3, pp. 355–368 (August 2007).     

Masses of the local group and of the M81 group estimated from distortions in the local velocity field

Based on high precision measurements of the distances to nearby galaxies with the Hubble telescope, we have determined the radii of the zero velocity spheres for the local group, R₀ = 0.96±0.03Mpc, and for the group of galaxies around M 81/M 82, 0.89±0.05Mpc. These yield estimates of M_T = (1.29±0.14)· 10¹² M_⊙ and (1.03±0.17)· 10¹² M_⊙, respectively, for the total masses of these groups. The R₀ method allows us to determine the mass ratios for the two brightest members in both groups, as well. By varying the position of the center of mass between the two principal members of a group to obtain minimal scatter in the galaxies on a Hubble diagram, we find mass ratios of 0.8:1.0 for our galaxy and Andromeda and 0.54:1.00 for the M82 and M81 galaxies, in good agreement with the observed ratios of the luminosities of these galaxies. __________ Translated from Astrofizika, Vol. 49, No. 1, pp. 5–22 (February 2006).