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1.
We present observations and first results from the FIGGS2 survey. FIGGS2 is an extension of the earlier Faint Irregular Galaxies GMRT survey (FIGGS) towards faint luminosity end. The sample consists of 20 galaxies, 15 of which were detected in HI 21 cm line using the Giant Meterwave Radio Telescope (GMRT). The median blue band magnitude of our sample is approximately ?11.m 6, which is more than one magnitude fainter than earlier FIGGS survey. From our GMRT observations we found that, for many of our sample galaxies, the HI disks are offset from their optical disks. The HI diameters of the FIGGS2 galaxies show a tight correlation with their HI mass. The slope of the correlation is 2.08 ± 0.20 similar to what is found for FIGGS galaxies. We also found that for almost all galaxies, the HI disks are larger than the optical disks which is a common trend for dwarf or spiral galaxies. The mean value of the ratio of HI to optical diameter is about 1.54.  相似文献   

2.
Knowledge of the molecular component of the ISM is fundamental to understand star formation. The H2 component appears to dominate the gas mass in the inner parts of galaxies, while the HI component dominates in the outer parts. Observation of the CO and other lines in normal and starburst galaxies have questioned the CO-to-H2 conversion factor, and detection of CO in dwarfs have shown how sensitive the conversion factor is to metallicity. Our knowledge has made great progress in recent years, because of sensitivity and spatial resolution improvements. Large-scale CO maps of nearby galaxies are now available, which extend our knowledge on global properties, radial gradients, and spiral structure of the molecular ISM. Millimetric interferometers reveal high velocity gradients in galaxy nuclei, and formation of embedded structures, like bars within bars. Galaxy interactions are very effective to enhance gas concentrations and trigger starbursts. Nuclear disks or rings are frequently observed, that concentrate the star formation activity. Since the density of starbursting galaxies is strongly increasing with redshift, the CO lines and the mm dust emission are a privileged tool to follow evolution of galaxies and observe the ISM dynamics at high redshift: they could give an answer about the debated question of the star-formation history, since many massive remote starbursts could be dust-enshrouded.  相似文献   

3.
Using the potential-density phase shift approach developed by the present authors in earlier publications, we estimate the magnitude of radial mass accretion/excretion rates across the disks of six nearby spiral galaxies (NGC 628, NGC 3351, NGC 3627, NGC 4321, NGC 4736, and NGC 5194) having a range of Hubble types. Our goal is to examine these rates in the context of bulge building and secular morphological evolution along the Hubble sequence. Stellar surface density maps of the sample galaxies are derived from SINGS 3.6 μm and SDSS i-band images using colors as an indicator of mass-to-light ratios. Corresponding molecular and atomic gas surface densities are derived from published CO (1-0) and HI interferometric observations of the BIMA SONG, THINGS, and VIVA surveys. The mass flow rate calculations utilize a volume-type torque integral to calculate the angular momentum exchange rate between the basic state disk matter and what we assume to be density wave modes in the observed galaxies. This volume-type integral contains the contributions from both the gravitational surface torque couple and the advective surface torque couple at the nonlinear, quasi-steady state of the wave modes, in sharp contrast to its behavior in the linear regime, where it contains only the contribution from the gravitational surface torque couple used by Lynden-Bell & Kalnajs in 1972. The potential-density phase shift approach yields angular momentum transport rates several times higher than those estimated using the Lynden-Bell and Kalnajs approach. And unlike Lynden-Bell and Kalnajs, whose approach predicts zero mass redistribution across the majority of the disk surface (apart from the isolated locations of wave-particle resonances) for quasi-steady waves, the current approach leads to predictions of significant mass redistribution induced by the quasi-steady density wave modes, enough for the morphological types of disks to evolve substantially within its lifetime. This difference with the earlier conclusions of Lynden-Bell and Kalnajs reflects the dominant role played by collisionless shocks in the secular evolution of galaxies containing extremely non-linear, quasi-steady density wave modes, thus enabling significant morphological transformation along the Hubble sequence during a Hubble time. We show for the first time also, using observational data, that stellar mass accretion/excretion is just as important, and oftentimes much more important, than the corresponding accretion/excretion processes in the gaseous component, with the latter being what had been emphasized in most of the previous secular evolution studies.  相似文献   

4.
We have observed a small sample of powerful double radio sources (radio galaxies and quasars) at frequencies around 90 GHz with the Berkeley Illinois Maryland Association (BIMA) millimetre array, with the intention of constraining the resolved high-frequency spectra of radio galaxies. When combined with other sources we have previously observed and with data from the BIMA archive, these observations allow us for the first time to make general statements about the high-frequency behaviour of compact components of radio galaxies – cores, jets and hotspots. We find that cores in our sample remain flat-spectrum up to 90 GHz; jets in some of our targets are detected at 90 GHz for the first time in our new observations and hotspots are found to be almost universal, but show a wide range of spectral properties. Emission from the extended lobes of radio galaxies is detected in a few cases and shows rough consistency with the expectations from standard spectral ageing models, though our ability to probe this in detail is limited by the sensitivity of BIMA. We briefly discuss the prospects for radio galaxy astrophysics with Atacama Large Millimeter Array.  相似文献   

5.
Together with C+ and CO, C is an important reservoir of carbon in the interstellar medium. We present recent results on the ground state transition of atomic carbon at 492 GHz, and on submillimeter CO lines in nearby galaxies. We show that atomic carbon is a good tracer of molecular gas in spiral galaxy disks. It has also a contribution to the molecular gas cooling: the cooling due to C and CO are of the same order of magnitude, and amounts typically to 4× 10-5 of the FIR continuum. C and CO cooling becomes significant in ULIRG galaxies like Arp220.It is possible to use CI measurements to diagnose the physical conditions in galaxies. Together with CII/CI, the emissivity ratio CI/FIR can be used as a measure of the non-ionizing UV radiation field in galaxies.  相似文献   

6.
We analyze the R-and K s-band photometric profiles for two independent samples of edge-on galaxies. The thickness of old stellar disks is shown to be related to the relative masses of the spherical and disk components of galaxies. The radial-to-vertical scale length ratio for galactic disks increases (the disks become thinner) with increasing total mass-to-light ratio of the galaxies, which reflects the relative contribution of the dark halo to the total mass, and with decreasing central deprojected disk brightness (density). Our results are in good agreement with numerical models of collisionless disks that evolved to a marginally stable equilibrium state. This suggests that, in most galaxies, the vertical stellar-velocity dispersion, on which the equilibrium-disk thickness depends, is close to a minimum value that ensures disk stability. The thinnest edge-on disks appear to be low-brightness galaxies in which the dark-halo mass far exceeds the stellar-disk mass.  相似文献   

7.
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.  相似文献   

8.
We examine the star formation properties of galaxies with very thin disks selected from the Revised FlatGalaxy Catalog (RFGC). The sample contains 333 ultra-flat galaxies (UFG) at high Galactic latitudes, |b| > 10?, with a blue major angular diameter of a ≥ 1.'2, blue and red apparent axial ratios of (a/b)b > 10, (a/b)r > 8.5 and radial velocities within 10 000 kms?1. As a control sample for them we use a population of 722 more thick RFGC galaxies with (a/b)b > 7, situated in the same volume. The UFG distribution over the sky indicates them as a population of quite isolated galaxies.We found that the specific star formation rate, sSFR FUV, determined via the FUV GALEX flux, increases steadily from the early type to late type disks for both the UFG and RFGC–UFG samples, showing no significant mutual difference within each morphological type T. The population of UFG disks has the average HI-mass-to-stellarmass ratio by (0.25 ± 0.03) dex higher than that of RFGC–UFG galaxies. Being compared with arbitrary orientated disks of the same type, the ultra-flat edge-on galaxies reveal that their total HI mass is hidden by self-absorption on the average by approximately 0.20 dex.We demonstrate that using the robust stellar mass estimate via 〈B?K〉-color and galaxy type T for the thin disks, together with a nowaday accounting for internal extinction, yields their sSFR quantities definitely lying below the limit of ?9.4 dex (yr?1). The collected observational data on UFG disks imply that their average star formation rate in the past has been approximately three times the current SFR. The UFG galaxies have also sufficient amount of gas to support their observed SFR over the following nearly 9 Gyrs.  相似文献   

9.
We address current theories of research on morphology, environment and evolution of active galaxies in the form of a detailed case study of the nearby QSO host I Zw 1. This study is based on sub-kpc resolution 12CO(1-0) observations with the BIMA mm-interferometer and on near-infrared imaging with ISAAC at the VLT. The 12CO(1-0) maps reveal a circumnuclear molecular gas ring with a radius of 0.9 kpc. The imaging data in the J-band are analyzed with respect to a disk-bulge decomposition. Together with a model of the gas rotation curve, the radial profile of the dynamical J-band mass-to-light ratio (M/L) is discussed. The J-band images give new evidence for an interaction between I Zw 1 and its nearby companion. First results from a sequence of N-body simulations for an extensive test of the parameter space of the interaction are presented. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

10.
We consider the relationship between the total HI mass in late-type galaxies and the kinematic properties of their disks. The mass MHI for galaxies with a wide variety of properties, from dwarf dIrr galaxies with active star formation to giant low-brightness galaxies, is shown to correlate with the product VcR0 (Vc is the rotational velocity, and R0 is the radial photometric disks cale length), which characterizes the specific angular momentum of the disk. This correlation, along with the decrease in the relative mass of the gas in a galaxy with increasing Vc, can be explained in terms of the previous assumption that the gas density in the disks of most galaxies is maintained at a level close to the threshold (marginal) stability of a gaseous layer to local gravitational perturbations. In this case, the regulation mechanism of the star formation rate associated with the growth of local gravitational instability in the gaseous layer must play a crucial role in the evolution of the gas content in the galactic disk.  相似文献   

11.
The [CII (158 μm)] fine structure line, which is the principal cooling line of the atomic gas, in two nearby galaxies observed with LWS on board ISO is compared to dust and HI gas emission and heating intensity. The relation between photoelectric effect on different grains populations, dust and gas heating found for a sample of 60 normal galaxies for which global [CII] measurements are available, still holds on scale of ～1.5 kpc. We also succeed in detecting cooling from a low density diffuse atomic gas associated with the diffuse optical disk in both galaxies, accounting typically for ～ 30–40% of the total [CII] emission.  相似文献   

12.
We present results from the BIMA survey of 12CO(1→0)emission from M33. The survey resolves this emission into individualobjects making this study the first unbiased, complete census of giantmolecular clouds (GMCs) in a spiral galaxy. The GMCs are clearlyassociated with dense atomic gas, suggesting formation from the HI. Moreover, high resolution observations of these clouds show thatthey appear the same as Milky Way GMCs when viewed through the sameobservational filters. The GMCs show significantly less angularmomentum than predicted by simple formation theories, suggesting theimportance of magnetohydrodynamic effects in their formation.  相似文献   

13.
The gas properties of barred and unbarredspiral galaxies are compared in two complete samples.It is found that two types of spiral galaxies do notdiffer to each other in atomic and molecular gascontents. On average there is 6 times more HI thanH2 in spiral galaxies and the ratio MHI/MH2decreases from early to late types. The barred andunbarred spirals in general show a similar behaviorsof the gas-to-luminosity relationships, but also thereare certain differences between them such ascorrelation of two gas phases (HI and H2) forunbarred galaxies. It is suggested that differentbehaviors of two types galaxies are due to the higherstar forming activity of barred with respect unbarredspirals. The expected values of HI and H2 gascontents have been estimated using blue and far-infrared emission.  相似文献   

14.
Elias Brinks   《New Astronomy Reviews》2004,48(11-12):1305
The SKA will revolutionise the study of the principles underlying star formation (SF), resolving interstellar cloud complexes which are the birthplaces of stars and answering such questions as which are the sufficient and necessary conditions for SF to commence. Also, massive SF is intimately related to stellar death. The SKA will be able to study the structure of the ISM at 100 pc resolution out to distances of up to 20 Mpc and will quantify the impact the demise of massive stars has on their environment. Importantly, the SKA will probe the transition region between ISM and IGM, linking star formation and stellar death in the disks of galaxies to faint HI structures further afield, such as “anomalous gas” and (Compact) High Velocity Clouds. Lastly, the superb sensitivity of the SKA will result in some hundred background sources per square degree against which HI absorption lines can be searched for, probing not only the relative importance of the different phases of the gas in galaxies but also the low density gas in the outskirts and between galaxies.  相似文献   

15.
The gas properties of barred and unbarred spiral galaxies are compared in two complete samples. It is found that two types of spiral galaxies do not differ from each other in atomic and molecular gas contents. On average there is 6 times more HI than H2 in spiral galaxies and the ratio MH2/MHI decreases from early to late types. The barred and unbarred spirals in general show a similar behaviors of the gas-to-luminosity relationships, but also there are certain differences between them such as correlation of two gas phases (HI and H2)for unbarred galaxies. It is suggested that different behaviors of two types galaxies are due to the higher star forming activity of barred with respect unbarred spirals. The expected values of HI and H2 gas contents have been estimated using blue and far-infrared emission. Published in Astrofizika, Vol. 43, No. 3, pp. 405-410, July–September, 2000.  相似文献   

16.
The HI content of galaxies in the Eridanus group is studied using the GMRT observations and the HIPASS data. A significant HI deficiency up to a factor of 2–3 is observed in galaxies in the high galaxy density regions. The HI deficiency in galaxies is observed to be directly correlated to the local projected galaxy density, and inversely correlated to the line-of-sight radial velocity. Furthermore, galaxies with larger optical diameters are predominantly in the lower galaxy density regions. It is suggested that the HI deficiency in Eridanus is due to tidal interactions. In some galaxies, evidences of tidal interactions are seen. An important implication is that significant evolution of galaxies can take place in the group environment. In the hierarchical way of formation of clusters via mergers of groups, a fraction of the observed HI deficiency in clusters could have originated in groups. The co-existence of S0s and severely HI deficient galaxies in the Eridanus group suggests that tidal interaction is likely to be an effective mechanism for transforming spirals to S0s.  相似文献   

17.
《New Astronomy Reviews》2002,46(2-7):279-282
We present 3-band HST imaging of three nearby (z<0.1) compact symmetric objects: 4C31.04, 1946+708 and 1146+596 (NGC 3894). These objects were chosen for HST observation on the basis of detected HI and molecular line absorption. The images show large amounts of obscuration in each source, well distributed throughout the host galaxies, but somewhat concentrated in the nuclear regions. All three also show evidence of nuclear structures which resemble disks or tori. We discuss the possible association of the nuclear structures and obscuration with their radio structures, and compare with other HST observations of GPS, CSS and large-scale radio galaxies.  相似文献   

18.
We have investigated the central regions of the galaxies in the NGC 3169/NGC 3166/NGC 3156 group with the multipupil fiber spectrograph of the 6-m telescope; the first (central) galaxy in the group is a spiral (Sa) one and the other two galaxies are lenticular ones. The group is known to have an extended HI cloud with a size of more than 100 kpc that is associated in its position, orientation, and rotation with the central galaxy NGC 3169. The mean age of the stellar populations in the centers of all three galaxies has been found to be approximately the same, ～1 Gyr. Since the galaxies are early-type ones and since NGC 3166 and NGC 3156 show no global star formation, we are dealing here with a synchronous star formation burst in the centers of all three galaxies.  相似文献   

19.
We investigate the process of galaxy formation as can be observed in the only currently forming galaxies - the so-called Tidal Dwarf Galaxies, hereafter TDGs - through observations of the molecular gas detected via its CO (Carbon Monoxide) emission. These objects are formed of material torn off of the outer parts of a spiral disk due to tidal forces in a collision between two massive galaxies. Molecular gas is a key element in the galaxy formation process, providing the link between a cloud of gas and a bona fide galaxy. We have detected CO in 8 TDGs (Braine, Lisenfeld, Duc and Leon, 2000: Nature 403, 867; Braine, Duc, Lisenfeld, Charmandaris, Vallejo, Leon and Brinks: 2001, A&A 378, 51), with an overall detection rate of 80%, showing that molecular gas is abundant in TDGs, up to a few 108 M ⊙. The CO emission coincides both spatially and kinematically with the HI emission, indicating that the molecular gas forms from the atomic hydrogen where the HI column density is high. A possible trend of more evolved TDGs having greater molecular gas masses is observed, in accord with the transformation of HI into H2. Although TDGs share many of the properties of small irregulars, their CO luminosity is much greater (factor ∼ 100) than that of standard dwarf galaxies of comparable luminosity. This is most likely a consequence of the higher metallicity (≳sim 1/3 solar) of TDGs which makes CO a good tracer of molecular gas. This allows us to study star formation in environments ordinarily inaccessible due to the extreme difficulty of measuring the molecular gas mass. The star formation efficiency, measured by the CO luminosity per Hα flux, is the same in TDGs and full-sized spirals. CO is likely the best tracer of the dynamics of these objects because some fraction of the HI near the TDGs may be part of the tidal tail and not bound to the TDG. Although uncertainties are large for individual objects, as the geometry is unknown, our sample is now of eight detected objects and we find that the ‘dynamical’ masses of TDGs, estimated from the CO line widths, seem not to be greater than the ‘visible’ masses (HI + H2 + a stellar component). Although higher spatial resolution CO (and HI) observations would help reduce the uncertainties, we find that TDGs require no dark matter, which would make them the only galaxy-sized systems where this is the case. Dark matter in spirals should then be in a halo and not a rotating disk. Most dwarf galaxies are dark matter-rich, implying that they are not of tidal origin. We provide strong evidence that TDGs are self-gravitating entities, implying that we are witnessing the ensemble of processes in galaxy formation: concentration of large amounts of gas in a bound object, condensation of the gas, which is atomic at this point, to form molecular gas and the subsequent star formation from the dense molecular component. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

20.
We present the results of study of the ionized gas velocity fields in 28 nearby (systemic velocity below 1000 km s?1) dwarf galaxies. The observations were made at the 6-m BTA telescope of the SAO RAS with the scanning Fabry-Perot interferometer in the Hα emission line. We were able to measure regular circular rotation parameters in 25 galaxies. As a rule, rotation velocities measured in HII are in a good agreement with the data on the HI kinematics at the same radii. Three galaxies reveal position angles of the kinematic axis in the HII velocity fields that strongly (tens of degrees) differ from the measurements in neutral hydrogen at large distances from the center or from the orientation of the major axis of optical isophotes. The planes of the gaseous and stellar disks in these galaxies most likely do not coincide. Namely, in DDO99 the gaseous disk is warped beyond the optical radius, and in UGC3672 and UGC8508 the inclination of orbits of gas clouds varies in the inner regions of galaxies. It is possible that the entire ionized gas in UGC8508 rotates in the plane polar to the stellar disk.  相似文献   

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