(Abridged) We present a comprehensive analysis of the relationship between star formation rate surface density (SFR SD) and gas surface density (gas SD) at sub-kpc resolution in a sample of 18 nearby galaxies. We use high resolution HI data from THINGS, CO data from HERACLES and BIMA SONG, 24 micron data from the Spitzer Space Telescope, and UV data from GALEX. We target 7 spiral galaxies and 11 late-type/dwarf galaxies and investigate how the star formation law differs between the H2-dominated centers of spiral galaxies, their HI-dominated outskirts and the HI-rich late-type/dwarf galaxies.
We find that a Schmidt-type power law with index N=1.0+-0.2 relates the SFR SD and the H2 SD across our sample of spiral galaxies, i.e., that H2 forms stars at a constant efficiency in spirals. The average molecular gas depletion time is ~2*10^9 yrs. We interpret the linear relation and constant depletion time as evidence that stars are forming in GMCs with approximately uniform properties and that the H2 SD may be more a measure of the filling fraction of giant molecular clouds than changing conditions in the molecular gas.
The relationship between total gas SD and SFR SD varies dramatically among and within spiral galaxies. Most galaxies show little or no correlation between the HI SD and the SFR SD. As a result, the star formation efficiency (SFE = SFR SD / gas SD) varies strongly across our sample and within individual galaxies. We show that in spirals the SFE is a clear function of radius, while the dwarf galaxies in our sample display SFEs similar to those found in the outer optical disks of the spirals. Another general feature of our sample is a sharp saturation of the HI SD at ~9 M_sol/pc^2 in both the spiral and dwarf galaxies.
We study the Milky Way region Z<3.0 kpc, where the thick disk and inner halo overlap, by using the kinematics of local blue horizontal branch (BHB) stars (within 1 kpc) and new samples of BHB stars and A-type stars from the Century Survey. We derive Galactic U,V,W velocities for these BHB and A-type star samples using proper motions from the NOMAD catalog. The mean velocities and the velocity dispersions of the BHB samples (Z<3 kpc) are characteristic of the halo, while those of the Century Survey A-type stars are characteristic of the thick disk. There is no evidence from our samples that the…
If typical gamma-ray bursts (GRBs) have X-ray counterparts similar to those detected by Ginga, then sensitive focusing X-ray telescopes will be able to detect GRBs three orders of magnitude fainter than the detection limit of the Burst and Transient Source Experiment (BATSE). If a substantial portion of the burst population detected by BATSE originates in a Galactic halo at distances greater than or equal to 150 kpc, existing X-ray telescopes will be able to detect GRBs in external galaxies out to a distance of at least 4.5 Mpc. As reported in Gotthelf, Hamilton, & Helfand (1996) the Imaging P…
We present the results of a VLA and WSRT search for HI emission from the vicinity of seven nearby clouds, which were observed in Lya absorption with HST toward Mrk335, Mrk501 and PKS2155-304. We searched a volume of 40' x 40' x 1000 km/s. The HI mass sensitivity (5 sigma) varies from 5x10^6 to 5x10^8 Msun. We detected HI emission in the vicinity of four out of seven absorbers. The closest galaxy is a small dwarf galaxy at a projected distance of 68/h kpc from the sight line toward Mrk335. It has the same velocity (V=1970 km/s) as one of the absorbers, and has an HI mass of only 4x10^7 Msun. We…
An all-sky list of 88 nearby dwarf spheroidal (dSph) galaxies with distances D < 10 Mpc is considered. Most of the objects have recently been found by Karachentseva & Karachentsev based on POSSII/ESO-SERC survey. A hundred more dSph galaxies are expected in this volume, being missed so far because of their low luminosity and low surface brightness. Apart from 22 dSph members of the Local Group, there are 33 dSphs in other nearby groups that have been resolved recently into stars with HST. Only 5% of the local dSphs are situated outside the known groups. We discuss observational correlation bet…
We measure the extent of 100 micron galactic emission in two independent galaxy samples using the IRAS 100 micron Sky Survey images and constrain the distribution of dust at large ($\ltsim$30 kpc) radii. The first sample consists of 90 nearby (v < 6000 km/s) galaxies from the RC3 catalog with similar angular sizes and absolute luminosities (5 arcmin $\leq $D$_{25} \leq$ 10 arcmin and $-22.5 \leq $M$_{B} \leq -18$) that are isolated in the 100 micron images. The second sample consists of 24 local galaxies (v < 1500 km/s, 10 arcmin $\leq $D$_{25} \leq$ 30 arcmin). We rescale the 100 micron image…
High resolution (a few arcseconds) observations of CO(1-0) and HCN(1-0) emission from nearby Seyfert galaxies have been conducted with the Nobeyama Millimeter Array. Based on the observed CO distributions and kinematics,we suggest that a small scale (a few 100 pc - a few kpc) distortion of the underlying potential seems to be necessary for Seyfert activity, although it is not a sufficient condition. We also find that the Toomre's Q values in the centers of Seyfert galaxies tend to be larger than unity, indicating the circumnuclear molecular gas disks around Seyfert nuclei would be gravitationa…
We are currently carrying out a K_s band survey for core-collapse supernovae in the nuclear (central kpc) regions of nearby starburst galaxies with the INGRID near-IR camera at the WHT. In this article we concentrate in describing mainly the observations and the real time processing of the SN search data, which makes use of the ING's integrated data flow system.
Gaia will play an important role in providing information about star formation histories, merging events, intergalactic streams etc., for nearby galaxies of the Local Group. One of the most crucial contributions will be proper motions, especially for stars in the outermost parts of the galaxies, obtainable for stellar populations to ~150 kpc with RGB stars. Together with radial velocities for the brightest giants <80 kpc, this will provide membership information for individual stars and global kinematical picture of the most nearby galaxies, including the Magellanic Clouds (MCs). Gaia will als…
We present the first results of a survey designed to understand the origin of the Lyman alpha-forest absorption systems at low redshift. Using the WYFFOS and HYDRA multi-fibre spectrographs on the WHT and WIYN telescopes, we have identified 51 galaxies brighter than b_j=18.5 within 30 arcmins of the sightline of the QSO 1821+643. We find three galaxies within 500 h-1 kpc of the QSO sightline; the nearest galaxy is 104 h-1 kpc away from the line of sight, and is at the same redshift as a strong Lyman alpha absorption line. The remaining two galaxies have no corresponding absorption to extremely…
Li abundances are derived for a sample of bulgelike stars with isochronal ages of 10-11 Gyr. These stars have orbits with pericentric distances, Rp, as small as 2-3 kpc and Zmax < 1 kpc. The sample comprises G and K dwarf stars in the metallicity range -0.80<[Fe/H]< +0.40. Few data of Li abundances in old turn-off stars (> 4.5 Gyr) within the present metallicity range are available. M67 (4.7 Gyr) and NGC 188 (6 Gyr) are the oldest studied metal-rich open clusters with late-type stars. Li abundances have also been studied for few samples of old metal-rich field stars. In the present work a high…
Observations with the Wide-Field Camera of the Hubble Space Telescope are presented for a representative sample of 20 intrinsically luminous quasars with redshifts smaller than 0.30. These observations show that luminous quasars occur in diverse environments that include ellipticals as bright as the brightest cluster galaxies (2), apparently normal ellipticals (10), apparently normal spirals with H II regions (3), complex systems of gravitationally interacting components (3), and faint surrounding nebulosity (2). The quasar host galaxies are centered on the quasar to the accuracy of our measur…
With the recent advent of large interferometric surveys, we can now probe the physical conditions, dynamics, and star-forming properties of molecular gas in the central kpc of starbursts and active galactic nuclei. We present results from the high-resolution (~ 100 pc) interferometric survey of molecular gas in the inner kpc of nearby starbursts (Jogee, Kenney, and Scoville 2001a) and the ongoing multi-transition survey of cold, warm, and dense molecular gas in a broad range of active and inactive galactic nuclei (Jogee, Baker, Sakamoto, and Scoville 2001b).
We analyze the statistical properties of the circumnuclear HII regions of a sample of 52 nearby galaxies ($v < 1000km/s) from archival HST/NICMOS H-band and Pa alpha (1.87micron) observations at unprecedented spatial resolutions of between 1 and 30pc. We find HII regions in the central regions of most galaxies, and more than a hundred in 8 galaxies. In contrast to disk HII regions, the physical properties (luminosity and size) of individual circumnuclear HII regions do not vary strongly with the morphological type of the host galaxy, nor does the number of circumnuclear HII regions per unit ar…
We report near-infrared photometry, spectroscopy, and speckle imaging of the hot, luminous star we identify as candidate LBV 1806-20. We also present photometry and spectroscopy of 3 nearby stars, which are members of the same star cluster containing LBV 1806-20 and SGR 1806-20. The spectroscopy and photometry show that LBV 1806-20 is similar in many respects to the luminous ``Pistol Star'', albeit with some important differences. They also provide estimates of the effective temperature and reddening of LBV 1806-20, and confirm distance estimates, leading to a best estimate for the luminosity …
Deep g'r'i'z' images obtained with the Gemini Multi-Object Spectrograph are used to investigate the stellar content in the outer regions of the nearby Sc galaxies NGC 2403 and M33. The red giant branch tip occurs at i' = 23.6 +/- 0.1 in NGC 2403, and the Cepheid and RGB-tip distance scales for this galaxy are in good agreement. While very young stars are restricted to radii < 10 kpc along the plane of the disk, a population of bright asymptotic giant branch (AGB) stars is present out to r = 20 kpc, indicating that star formation occured outside of the present-day star-forming disk of NGC 2403 …
I review studies of the hot gaseous medium in and around nearby normal disk galaxies, including the Milky Way. This medium represents a reservoir of materials required for lasting star formation, a depository of galactic feedback (e.g., stellar mass loss and supernovae), and an interface between the interstellar and intergalactic media. Important progress has been made recently with the detection of X-ray absorption lines in the spectra of X-ray binaries and AGNs. The X-ray absorption line spectroscopy, together with existing X-ray emission and far-UV \ovi absorption measurements now allows fo…
We investigate the relations among the stellar continuum-subtracted 8 micron polycyclic aromatic hydrocarbon (PAH 8 micron) emission, 24 micron hot dust emission, and 160 micron cold dust emission in fifteen nearby face-on spiral galaxies in the Spitzer Infrared Nearby Galaxies Survey sample. The relation between PAH 8 and 24 micron emission measured in ~2 kpc regions is found to exhibit a significant amount of scatter, and strong spatial variations are observed in the (PAH 8 micron)/24 micron surface brightness ratio. In particular, the (PAH 8 micron)/24 micron surface brightness ratio is obs…
Shock heating by radio jets is potentially an important process in a range of environments, as it will increase the entropy of the heated gas. Although this process is expected to occur in the most powerful radio-loud AGN, strong shocks have so far only been detected in nearby low-power radio galaxies. Here we discuss X-ray detections of strong shocks in nearby galaxies, including a new detection of shocked gas around both lobes of the nearby radio galaxy NGC 3801 with inferred Mach numbers of 3 - 6 and a total injected energy comparable to the thermal energy of the ISM within 11 kpc. We discu…
Maps and measurements of the J=1-0, J=2-1, J=3-2, J=4-3 12CO, the J=1-0, J=2-1, and J=3-2 13CO lines in the central arcminute squared of NGC1068, NGC2146, NGC3079, NGC4826, and NGC7469, as well as 492 GHz [CI] maps in three of these are used to model the circumnuclear molecular gas in these galaxies. In all five objects, the bright CO concentrations mapped have line intensities that require two distinct gas components for satisfactory fits. The physical condition of the molecular gas differs from galaxy to galaxy. High kinetic temperatures of 125-150 K occur in NGC2146 and NGC3079. Very high d…
Fast (~1000 km/s) outflows of neutral gas (from 21-cm HI absorption) are detected in strong radio sources. The outflows occur, at least in some cases, at distances from the radio core that range between few hundred parsecs and kpc. These HI outflows likely originate from the interaction between radio jets and the dense surrounding medium. The estimated mass outflow rates are comparable to those of moderate starburst-driven superwinds. The impact on the evolution of the host galaxies is discussed.
This paper reviews the evidence for interaction between radio jets and their environment in small and intermediate (sub-kpc) scale radio sources. Observations of gas (both neutral hydrogen and ionised gas) have shown the presence of fast (> 1000 km/s) outflows likely originating from this interaction. The characteristics of these AGN-driven outflows (e.g. mass outflow rate) indicate that they may have a relevant impact on the evolution of the host galaxy. We also report on the detection of large HI disks found around the host galaxies of nearby compact radio sources. Similar structures have so…
We present the latest results from our project to search for new planetary nebulae in nearby galaxies using Sloan Digital Sky Survey (SDSS) imaging data. Our method is based on photometric criteria and can be applied to galaxies where PNe appear as point sources. We applied these criteria to the whole area of M31 as scanned by SDSS, detecting 130 new PN candidates and 30 known PNe. All selected PNe candidates are located in the outer regions of M31. For 85 candidates follow-up spectroscopy was obtained with the 2.2m telescope at Calar Alto Observatory. The observations show that our method has…
We present results from an analysis of two Chandra observations of the rich, nearby galaxy cluster Abell 2199. We find evidence (having corrected for projection effects) for radial gradients in temperature and metallicity in the X-ray emitting gas: the temperature drops from kT~4.2 keV at R=200 kpc to 1.6 keV within R=5 kpc of the centre. The metallicity rises from ~0.3 solar at R=200 kpc to ~0.7 solar at R=30 kpc before dropping to 0.3 solar within the central 5 kpc. We find evidence for structure in the surface brightness distribution associated with the central radio source 3C338. No eviden…
We present the first sub-kpc 0.7" (~ 850 pc) resolution 12CO(1-0) molecular line observations of the ISM in the host galaxy of the QSO I Zw 1. The observations were obtained with the BIMA mm-interferometer in its compact A configuration. The BIMA data are complemented by new observations of the 12CO(2-1) and 13CO(1-0) line with IRAM Plateau de Bure mm-interferometer (PdBI) at 0.9" and 1.9" resolution, respectively. These measurements, which are part of a multi-wavelength study of the host galaxy of I Zw 1, are aimed at comparing the ISM properties of a QSO host with those of nearby galaxies as…
We have used STIS aboard HST to search for Lyman-alpha (Lya) absorption lines in the outer regions of eight nearby galaxies using background QSOs and AGN as probes. Lya lines are detected within a few hundred km/s of the systemic velocity of the galaxy in all cases. We conclude that a background line-of-sight which passes within 26-200 h-1 kpc of a foreground galaxy is likely to intercept low column density neutral hydrogen with log N(HI) >~ 13.0. The ubiquity of detections implies a covering factor of ~ 100% for low N(HI) gas around galaxies within 200 h-1 kpc. We discuss the difficulty in tr…
The X-ray properties of 15 nearby (v<3,000 km/s) galaxies that possess AGN and/or starbursts are discussed. Two-thirds have nuclear extended emission on scales from ~0.5 to ~1.5 kpc that is either clearly associated with a nuclear outflow or morphologically resembles an outflow. Galaxies that are AGN-dominated tend to have linear structures while starburst-dominated galaxies tend to have plume-like structures. Significant X-ray absorption is present in the starburst regions, indicating that a circumnuclear starburst is sufficient to block an AGN at optical wavelengths. Galaxies with starburst …
In this contribution, first results of deep VLT photometry (V,I) in the central region of the Hydra I and Centaurus galaxy clusters are presented. In both galaxy clusters, many star clusters have been identified down to the turnover magnitude of the globular cluster luminosity function at V=26.0 mag. They are distributed not only around the several early-type galaxies, but also in the intra-cluster field, as far as 250 kpc from the cluster centers. Outside the bulges of the central galaxies in Hydra I and Centaurus, the intra-cluster globular cluster system is dominated by blue clusters whose …
The discovery of a large population of intra-cluster star clusters in the central region of the Hydra I and Centaurus galaxy clusters is presented. Based on deep VLT photometry (V,I), many star clusters have been identified not only around the early-type galaxies, but also in the intra-cluster field, as far as 250 kpc from the galaxy centres. These intra-cluster globulars are predominantly blue, with a siginificant fraction being even bluer than the metal-poor halo clusters around massive galaxies. When interpreted as a metallicity effect they would have iron abundances around [Fe/H] = -2 dex.…
We examine the properties of central dust in nearby quiescent and active early-type galaxies. The active galaxies are low-power radio galaxies with Fanaroff & Riley Type I or I/II radio jets. We focus on the comparison of the dust distributions in the active and quiescent galaxy samples and the relation between the radio jet and dust orientations. Our main observational conclusions are: (a) radio galaxies contain a higher fraction of regular dust 'ellipses' compared to quiescent galaxies which contain more often irregular dust distributions; (b) the morphology, size and orientation of dust ell…
We present deep HI 21-cm and optical observations of the face-on spiral galaxy M 83 obtained as part of a project to search for high-velocity clouds (HVCs) in nearby galaxies. Anomalous-velocity neutral gas is detected toward M 83, with 5.6x10^7 Msolar of HI contained in a disk rotating 40-50 km/s more slowly in projection than the bulk of the gas. We interpret this as a vertically extended thick disk of neutral material, containing 5.5% of the total HI within the central 8 kpc. Using an automated source detection algorithm to search for small-scale HI emission features, we find eight distinct…
We present high-resolution VLA observations of the molecular gas in the host galaxy of the highest redshift quasar currently known, SDSS J1148+5251 (z=6.42). Our VLA data of the CO(3-2) emission have a maximum resolution of 0.17'' x 0.13'' (~1 kpc), and enable us to resolve the molecular gas emission both spatially and in velocity. The molecular gas in J1148+5251 is extended to a radius of 2.5 kpc, and the central region shows 2 peaks, separated by 0.3'' (1.7 kpc). These peaks account for about half of the total emission, while the remainder is more extended. Each of these unresolved peaks con…
We used V and I CCD photometry to search for low-surface brightness dwarf galaxies (LSBD) in the central (<0.5 h^-1 Mpc) region of the groups NGC 6868, NGC 5846, HCG 42 and the poor cluster IC 4765. Using the parameters given by the exponential profile fit, we identified 80 LSBD candidates with magnitudes 17 < V < 22 mag and with colors V-I < 1.5 mag at the limiting isophote of 25.8 V mag/arcsec^2. The galaxies have mu0 > 22.5 V mag/arcsec^2, h > 1.5 arcsec, and diameters larger than 1.2 h^-1 kpc. Twenty of the eighty galaxies are extended LSB galaxies that were detected only on smoothed image…
We present HI observations of the galaxies in the first list of the Karachentsev catalog of previously unknown nearby dwarf galaxies (Karachentseva & Karachentsev 1998). This survey covers all known nearby galaxy groups within the Local Volume (i.e. within 10 Mpc) and their environment, that is about 25% of the total sky. A total of 257 galaxies have been observed with a detection rate of 60%. We searched a frequency band corresponding to heliocentric radial velocities from -470 km/s to about +4000 km/s. Non-detections are either due to limited coverage in radial velocity, confusion with Local…
I present a study of the molecular gas and star formation (SF) properties in the inner few kpc of the brightest nearby M82-class starbursts and control non-starbursts, based on high resolution CO (J=1--0) observations, optical and NIR images, along with published radio continuum and Br-gamma data. I outline the marked differences between molecular gas in the inner kpc and outer disk of spiral galaxies in terms of gas surface densities, gas mass fractions, epicyclic frequencies, and velocity dispersions. One implication is that in the inner kpc, gravitational instabilities set in only at very h…
We present a new, complete, sample of 95 radio sources selected from the B2 and 3CR catalogues, with z < 0.1. Since no selection effect on the core radio power, jet velocity, or source orientation is present, this sample is well suited for statistical studies. In this first paper we present the observational status of all sources on the parsec (mas) and kiloparsec (arcsec) scale; we give new parsec-scale data for 28 sources and discuss their parsec-scale properties. Combining these data with those in the literature, information on the parsec-scale morphology is available for a total of 53 radi…
We present high-resolution (<0.7") ground-based images of the edge-on spiral galaxies NGC 891 (D=9.5 Mpc) and NGC 4013 (D=17 Mpc) acquired with the WIYN 3.5-m telescope. These BVI + H-alpha images reveal complex webs of dusty interstellar material far above the midplanes of both galaxies (0.5 < |z| < 2 kpc) as discussed previously by Howk & Savage (1997). The dusty high-z clouds, visible in absorption against the background stellar light of the galaxies, have widths 50-100 pc and lengths 100-400 pc. An analysis of their absorbing properties suggests they have A_V > 0.5 - 2.0. If Milky Way gas-…
We are conducting a deep near-infrared (NIR) imaging survey of young embedded clusters in the extreme outer Galaxy (hereafter EOG), at the Galactic radius (R_g) of more than 18 kpc. The EOG is an excellent laboratory to study the nature of the IMF in a low-metallicity environment with a great advantage of the proximity compared to nearby dwarf galaxies, such as LMC & SMC. As a first step, we obtained deep NIR images of Digel Cloud 2 clusters at R_g ~19 kpc using the Subaru 8.2-m telescope. The observed K-band luminosity function shows that IMF in the low metallicity environment down to ~ 0.1 M…
In spiral galaxies where the molecular phase dominates the ISM, the molecular gas as traced by CO emission will approximately obey the continuity equation on orbital timescales. The Tremaine-Weinberg method can then be used to determine the pattern speed of such galaxies. We have applied the method to single-dish CO maps of three nearby spirals, M51, M83 and NGC 6946 to obtain estimates of their pattern speeds: 38 +/- 7 km/s/kpc, 45 +/- 8 km/s/kpc and 39 +/- 8 km/s/kpc, respectively, and we compare these results to previous measurements. We also analyze the major sources of systematic errors i…
We present results of a study of neutral hydrogen (HI) in a complete sample of nearby non-cluster radio galaxies. We find that radio galaxies with large amounts of extended HI (M_HI >= 10^9 M_solar) all have a compact radio source. The host galaxies of the more extended radio sources, all of Fanaroff & Riley type-I, do not contain these amounts of HI. We discuss several possible explanations for this segregation. The large-scale HI is mainly distributed in disk- and ring-like structures with sizes up to 190 kpc and masses up to 2 x 10^10 M_solar. The formation of these structures could be rela…
We review recent observations of molecular gas in nearby galaxies and their implications for the star formation law on large (>1 kpc) scales. High-resolution data provided by millimetre interferometers are now adding to the basic understanding that has been provided by single-dish telescopes. In particular, they confirm the good correlation between star formation rate (SFR) and molecular gas surface densities, while at the same time revealing a greater degree of heterogeneity in the CO distribution. Galaxies classified as SAB or SB tend to show radial CO profiles that peak sharply in the inner…
In a new survey of nearby galaxies from stacked photographic images, M87 shows a diffuse fan of stellar material which extends along the projected SE (major) axis out to about 100 kpc at a limiting (B) surface brightness of $28 \hbox{mag arcsec}^{-2}$. We suggest that disruption of a small spheroidal galaxy within a larger potential is the most likely explanation for the diffuse structure. Our simulations include a rigid primary potential with characteristics similar to those derived for M87 and a populated intruder. The orbit is required to pass close to the center of the potential to produce…
We investigate the relationship between the star formation rate (SFR) and dense molecular gas mass in the nuclei of galaxies. To do this, we utilize the observed 850 micron luminosity as a proxy for the infrared luminosity and SFR, and correlate this with the observed CO (J=3-2) luminosity. We find tentative evidence that the LIR-CO (J=3-2) index is similar to the Kennicutt-Schmidt (KS) index (N ~ 1.5) in the central ~1.7 kpc of galaxies, and flattens to a roughly linear index when including emission from the entire galaxy. This result may imply that the volumetric Schmidt relation is the unde…
