R. Giovanelli

Cornell University, Ithaca, New York, United States

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Publications (173)359.64 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We present neutral hydrogen (HI) imaging observations with the Westerbork Synthesis Radio Telescope of AGC198606, an HI cloud discovered in the ALFALFA 21cm survey. This object is of particular note as it is located 16 km/s and 1.2 degrees from the gas-bearing ultra-faint dwarf galaxy Leo T while having a similar HI linewidth and approximately twice the flux density. The HI imaging observations reveal a smooth, undisturbed HI morphology with a full extent of 23'x16' at the 5x10^18 atoms cm^-2 level. The velocity field of AGC198606 shows ordered motion with a gradient of ~25 km/s across ~20'. The global velocity dispersion is 9.3 km/s with no evidence for a narrow spectral component. No optical counterpart to AGC198606 is detected. The distance to AGC198606 is unknown, and we consider several different scenarios: physical association with Leo T, a minihalo at a distance of ~150 kpc based on the models of Faerman et al. (2013), and a cloud in the Galactic halo. At a distance of 420 kpc, AGC198606 would have an HI mass of 6.2x10^5 Msun, an HI radius of 1.4 kpc, and a dynamical mass within the HI extent of 1.5x10^8 Msun.
    11/2014;
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    ABSTRACT: The ALFALFA Hα survey uses a volume-limited sample of HI-selected galaxies from the ALFALFA survey to study star formation in the local universe. When complete, this survey will have narrow-band Hα images of over 1500 HI-selected galaxies with velocities between 1500 km/s and 7500 km/s. ALFALFA detects galaxies with HI masses as low as ~3x10^7 M_sol in our survey volume, probing well into the flat portion of the HI mass function. With our unique data set we are able to study star formation in a sample of galaxies selected to be capable of making stars and are unbiased to the optical properties of the galaxies. Our primary science goal is to produce the best possible measurement of the local star-formation rate density. We also use our data set to study star formation as a function of galaxy environment and compare UV and Hα star-formation rates (using GALEX). The ALFALFA Hα survey is ongoing, but is complete in the fall sky. Here we present an overview of the entire survey and results based on the fall sample.
    06/2013;
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    ABSTRACT: A long standing problem in cosmology is the mismatch between the number of low mass dark matter halos predicted by simulations and the number of low mass galaxies observed in the Local Group. We recently presented a set of isolated ultra-compact high velocity clouds (UCHVCs) identified within the dataset of the Arecibo Legacy Fast ALFA (ALFALFA) HI line survey that are consistent with representing low mass gas bearing dark matter halos within the Local Group (Adams et al. 2013). At distances of ~1 Mpc, the UCHVCs have HI masses of ~10^5 Msun and indicative dynamical masses of ~10^7 Msun. The HI diameters of the UCHVCs range from 4' to 20', or 1 to 6 kpc at a distance of 1 Mpc. We have selected the most compact and isolated UCHVCs with the highest average column densities as representing the best galaxy candidates. We are undertaking an imaging campaign using pODI on the WIYN 3.5m telescope to search for resolved stellar counterparts to these UCHVCs. The central coverage region of pODI is well matched to the HI size of the UCHVCs and the outlying detectors allow a constraint on foreground and background contamination. Our g'- and i'-band observations allow us to probe to ~1.5 magnitude below the tip of the red giant branch out to distances of ~1 Mpc. We present preliminary results from the broadband imaging and discuss constraints on the stellar population of these objects. This work has been supported by NSF grants AST-0607007 and AST-1107390, grants from the Brinson Foundation, and a NSF GRFP.
    06/2013;
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    ABSTRACT: Structural parameters for 742 late-type galaxies in the Local and Coma Superclusters are presented. For each galaxy AGC and VCC (CGCG instead of VCC for Coma) names, equatorial coordinates and concentration, asymmetry and clumpiness computed in the r band are given. Where possible we provide also the CAS parameters from Halpha narrow-band images, and half-light radii from the r band, Halpha and EW(Halpha) maps. (2 data files).
    VizieR Online Data Catalog. 03/2013;
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    ABSTRACT: We present an update on the Survey of HI in Extremely Low-mass Dwarfs (SHIELD), a multi-configuration Very Large Array (VLA) study of the neutral gas contents and dynamics of galaxies with HI masses in the 106 - 107 M⊙ range detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. SHIELD is designed to address three primary questions: What properties change between HI clouds lacking optical counterparts, very low-mass dwarfs, and more massive systems? What fraction of the mass in these low-mass dwarfs is baryonic? And is the character of the star formation process different in very low-mass galaxies? We present high-resolution B-configuration HI imaging of a subset of the SHIELD sample, including detailed rotation analysis and HI distribution maps. This poster is the first in a series that analyzes new SHIELD observations; companion posters focus on results from imaging campaigns with the Hubble Space Telescope, the Spitzer Space Telescope, the Galaxy Evolution Explorer (GALEX), and the WIYN 3.5 m telescope.
    01/2013;
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    ABSTRACT: The Survey of HI in Extremely Low-mass Dwarfs (SHIELD) is an ongoing study of twelve galaxies with HI masses between 106 and 107 Solar masses, detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. The distribution of stellar mass in each system is a crucial component of our understanding of the baryonic and dark matter contents of these galaxies. Using Spitzer Space Telescope 3.6 and 4.5 micron imaging, we have measured the flux of each galaxy. In conjunction with distances derived from Hubble Space Telescope imaging, we have determined the stellar mass and its distribution as a function of radius for ten of the twelve systems.
    01/2013;
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    ABSTRACT: The ALFALFA survey recently discovered the galaxy Leo P, one of the most extreme low-mass star-forming dwarf galaxies in the local volume. We present new HI spectral line imaging of Leo P acquired with the Karl G. Jansky Very Large Array (VLA) in the B- and C-configurations. A peak column density of 2.5×1020 cm-2 is detected at 30 arcsecond resolution and is spatially coincident with the optical center. Diffuse, low column density HI emission extends to the Southeast. 40% of the ALFALFA flux was recovered by the C-configuration observations; a substantial fraction of the neutral gas component resides on scales larger than 30 arcseconds. A sparsely sampled rotation curve demonstrates that the neutral gas is kinematically complex on scales of ~100 pc. We estimate the dynamical mass Mdyn = 8×10^6 DMpc M⊙, where DMpc is the distance in Mpc. This can be compared with the total HI mass, MHI = 3×10^6 D^2 Mpc .
    American Astronomical Society Meeting Abstracts; 01/2013
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    ABSTRACT: We present KPNO 4-m and LBT/MODS spectroscopic observations of an HII region in the nearby dwarf irregular galaxy Leo P recently discovered in the Arecibo ALFALFA survey. In both observations, we were able to accurately measure the temperature sensitive [O III] λ4363 line, and thus determine oxygen abundances using the "direct" method. The oxygen abundance was found to be 12 + log(O/H) = 7.15 +/- 0.05. Thus, Leo P is an extremely metal deficient (XMD) galaxy, and, indeed, one of the most metal deficient galaxies ever observed. For its estimated luminosity, Leo P is consistent with the relationship between luminosity and oxygen abundance seen in nearby dwarf galaxies. Additionally, we derive relative abundances of N, S, Ne, Ar, and He and compare the relative abundances observed in Leo P to those observed in other XMD galaxies. Leo P shows normal alpha element abundances, but elevated N/O relative to other XMD galaxies. Finally, we derived a helium mass fraction of 0.2490 +/- 0.0146 which compares well with the WMAP + BBN prediction of 0.2487 +/- 0.0002 for the primordial helium abundance. We suggest that surveys of very low mass galaxies compete well with emission line galaxy surveys for finding XMD galaxies.
    01/2013;
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    ABSTRACT: The Survey of HI in Extremely Low-mass Dwarfs (SHIELD) is an ongoing study of twelve galaxies with HI masses between 106 and 107 Solar masses, detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. Here we present new Hubble Space Telescope (HST) imaging of the SHIELD galaxies. The primary goal is to determine the distance of each galaxy. We apply two techniques to measure the apparent magnitude of the tip of the red giant branch (TRGB) feature in the HST color magnitude diagrams. First, a custom designed edge detection filter was written to determine the TRGB magnitude based on a user-selected region of the color magnitude diagram. Second, we apply the maximum likelihood technique implemented in the "TRGBtool" software package (Makarov et al. 2006). In addition to the distances based on the TRGB feature, we also use the MATCH software (Dolphin 2002) to determine the best-fit distance based on the overall CMD morphology. We compare these distance estimates for all members of the SHIELD galaxies, and present a final table of distances that is used in each of the companion SHIELD presentations.
    01/2013;
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    ABSTRACT: The Survey of HI in Extremely Low-mass Dwarfs (SHIELD) is an ongoing study of twelve galaxies with HI masses between 106 and 107 Solar masses, detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. Here we present new WIYN 3.5m broad and narrow band optical imaging, and archival GALEX ultraviolet imaging, of the SHIELD sample. These data allow us to study star formation on very recent (<10 Myr) and on intermediate (few hundred Myr) timescales. A comparison of these two diagnostics confirms the trend of weak H alpha emission compared to the ultraviolet in low mass galaxies found by Lee et al. (2009). We also compare the H alpha and broad band images with the HI imaging obtained with the Very Large Array.
    01/2013;
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    ABSTRACT: Context. We present Hα3 (acronym for Hα - αα), an Hα narrow-band imaging survey of ~400 galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) in the Local Supercluster, including the Virgo cluster. Aims: By using hydrogen recombination lines as a tracer of recent star formation, we aim to investigate the relationships between atomic neutral gas and newly formed stars in different environments (cluster and field), morphological types (spirals and dwarfs), and over a wide range of stellar masses (~107.5 - 1011.5 M⊙). Methods: We image in Hα+[NII] all the galaxies that contain more than 107 M⊙ of neutral atomic hydrogen in the sky region 11h < RA < 16h; 4° < Dec < 16°; 350 < cz < 2000 km s-1 using the San Pedro Martir 2 m telescope. This survey provides a complete census of the star formation in HI rich galaxies of the local universe. Results: We present the properties of the galaxy sample, together with Hα fluxes and equivalent widths. We find an excellent agreement between the fluxes determined from our images in apertures of 3 arcsec diameter and the fluxes derived from the SDSS spectral database. From the Hα fluxes corrected for galactic and internal extinction and for [NII] contamination we derive the global star formation rates (SFRs). Observations taken at the observatory of San Pedro Martir (Baja California, Mexico), belonging to the Mexican Observatorio Astronómico Nacional.FITS images for all galaxies are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/545/A16
    Astronomy and Astrophysics 09/2012; · 5.08 Impact Factor
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    ABSTRACT: We present Hα3 (acronym for Hα-αα), an Hα narrow-band imaging survey of ~400 galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) in the Local Supercluster, including the Virgo cluster. By using hydrogen recombination lines as a tracer of recent star formation, we aim to investigate the relationships between atomic neutral gas and newly formed stars in different environments (cluster and field), morphological types (spirals and dwarfs), and over a wide range of stellar masses (~107.5-1011.5M⊙). We image in Hα+[NII] all the galaxies that contain more than 107M⊙ of neutral atomic hydrogen in the sky region 11h<R.A.<16h ; 4°<Dec.<16°; 350<cz<2000km/s using the San Pedro Martir 2m telescope. This survey provides a complete census of the star formation in HI rich galaxies of the local universe. We present the properties of the galaxy sample, together with Hα fluxes and equivalent widths. We find an excellent agreement between the fluxes determined from our images in apertures of 3-arcsec diameter and the fluxes derived from the SDSS spectral database. From the Hα fluxes corrected for galactic and internal extinction and for [NII] contamination we derive the global star formation rates (SFRs). (3 data files).
    VizieR Online Data Catalog. 05/2012;
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    ABSTRACT: We examine the global properties of the stellar and HI components of 229 low HI mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with HI masses < 10^{7.7} M_sun and HI line widths < 80 km s^{-1}. SDSS data are combined with photometric properties derived from GALEX to derive stellar masses (M_*) and star formation rates (SFRs) by fitting their UV-optical spectral energy distributions (SEDs). In optical images, many of the ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs) and estimates of their SFRs and M_* obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M_* < 10^8 M_sun is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo cluster. The imposition of an upper HI mass limit yields the selection of a sample with lower gas fractions for their M_* than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have HI depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation laws is consistent with the general assumptions that gas-rich galaxies have lower star formation efficiencies than do optically selected populations and that HI disks are more extended than stellar ones.
    The Astronomical Journal 03/2012; 143(6). · 4.97 Impact Factor
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    ABSTRACT: We are conducting COLD GASS, a legacy survey for molecular gas in nearby galaxies. Using the IRAM 30-m telescope, we measure the CO(1-0) line in a sample of ~350 nearby (DI~=100-200Mpc), massive galaxies (log(M*/M⊙)>10.0). The sample is selected purely according to stellar mass, and therefore provides an unbiased view of molecular gas in these systems. By combining the IRAM data with Sloan Digital Sky Survey (SDSS) photometry and spectroscopy, GALEX imaging and high-quality Arecibo HI data, we investigate the partition of condensed baryons between stars, atomic gas and molecular gas in 0.1-10L* galaxies. In this paper, we present CO luminosities and molecular hydrogen masses for the first 222 galaxies. Description: To overcome this issue, the GALEX Arecibo SDSS Survey (GASS; Catinella et al. 2010, Cat. J/MNRAS/403/683) was designed to measure the neutral hydrogen content for a large, unbiased sample of ~1000 massive galaxies (M*>1010M⊙), via longer pointed observations. GASS is a large programme currently under way at the Arecibo 305-m telescope, and is producing some of the first unbiased atomic gas scaling relations in the nearby Universe (Catinella et al. 2010, Cat. J/MNRAS/403/683; Schiminovich et al., 2010MNRAS.408..919S; Fabello et al., 2011MNRAS.411..993F). We are in the process of constructing a CO Legacy Data base for the GASS survey (COLD GASS), measuring the molecular gas content of a significant subsample of the GASS galaxies. We will then be able to quantify the link between atomic gas, molecular gas and stars in these systems. (1 data file).
    VizieR Online Data Catalog. 02/2012;
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    ABSTRACT: The "Survey of HI in Extremely Low-mass Dwarfs” is a systematic exploration of the neutral gas contents and dynamics of 12 ALFALFA-selected galaxies with HI masses between 106 and 107 solar masses. AGC 749237 is amenable to in-depth dynamical analysis using high spectral resolution (0.83 km s-1 ch-1) EVLA B and C configuration observations. Tilted ring analysis in GIPSY is performed at three spatial resolutions ( 81.5 pc, 163 pc, and 326 pc). While the small-scale kinematics indicate some non-circular motions, the extracted rotation curve flattens at 28±3 km s-1 at radii between 81.5 and 620.5 pc. From this we infer a total dynamical mass of (1.1±0.2)x108 solar masses.
    01/2012;
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    ABSTRACT: The Arecibo Legacy Fast ALFA (ALFALFA) blind neutral hydrogen survey is an ongoing project that includes an innovative undergraduate outreach component promoting the participation of students and faculty at undergraduate-focused institutions in a large, multi-year research collaboration. The survey, which will ultimately detect ˜30,000 gas-rich galaxies, provides resources and authentic opportunities for undergraduates and faculty, including a high fraction of women and minorities, through the Undergraduate ALFALFA Team (UAT), an NSF-sponsored consortium of 18 participating institutions. The UAT experience features annual workshops at the Arecibo Observatory with hands-on experience for undergrad participants and their faculty mentors. Graduate students on the Cornell ALFALFA Team help plan and facilitate UAT activities and benefit by developing their own skills as mentors, project supervisors, and science communicators. The UAT is developing online lesson plans and activity guides that make use of the ALFALFA online data archive and of innovative learning techniques supported by the findings of astronomy education research.
    09/2011;
  • 07/2011;
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    ABSTRACT: We use a stacking technique to measure the average HI content of a volume-limited sample of 1871 AGN host galaxies from a parent sample of galaxies selected from the SDSS and GALEX imaging surveys with stellar masses greater than 10^10 M_sun and redshifts in the range 0.025<z<0.05. HI data are available from the Arecibo Legacy Fast ALFA (ALFALFA) survey. In previous work, we found that the HI gas fraction in galaxies correlates most strongly with the combination of optical/UV colour and stellar surface mass density. We therefore build a control sample of non-AGN matched to the AGN hosts in these two properties. We study trends in HI gas mass fraction (M(HI)/M_*), where M_* is the stellar mass) as a function of black hole accretion rate indicator L[OIII]/M(BH). We find no significant difference in HI content between AGN and control samples at all values of black hole accretion rate probed by the galaxies in our sample. This indicates that AGN do not influence the large-scale gaseous properties of galaxies in the local Universe. We have studied the variation in HI mass fraction with black hole accretion rate in the blue and red galaxy populations. In the blue population, the HI gas fraction is independent of accretion rate, indicating that accretion is not sensitive to the properties of the interstellar medium of the galaxy on large scales. However, in the red population accretion rate and gas fraction do correlate. The measured gas fractions in this population are not too different from the ones expected from a stellar mass loss origin, implying that the fuel supply in the red AGN population could be a mixture of mass loss from stars and gas present in disks.
    04/2011;
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    ABSTRACT: This is the second paper of two reporting results from a study of the HI content and stellar properties of nearby galaxies detected by the Arecibo Legacy Fast ALFA blind 21-cm line survey and the Sloan Digital Sky Survey in a 2160 deg^2 region covered by both surveys. We apply strategies of multivariate data analysis to a complete HI flux-limited subset of 1624 objects extracted from the control sample of HI emitters assembled by Toribio et al. (2011a) in order to: i) investigate the correlation structure of the space defined by an extensive set of observables describing gas-rich systems; ii) identify the intrinsic parameters that best define their HI content; and iii) explore the scaling relations arising from the joint distributions of the quantities most strongly correlated with the HI mass. The principal component analysis performed over a set of five galaxy properties reveals that they are strongly interrelated, supporting previous claims that nearby HI emitters show a high degree of correlation. The best predictors for the expected value of MHI are the diameter of the stellar disk, D25r, followed by the total luminosity (both in the r-band), and the maximum rotation speed, while morphological proxies such as color show only a moderately strong correlation with the gaseous content attenuated by observational error. The simplest and most accurate prescription is log(MHI/Msun)= 8.72 + 1.25*log(D25r/kpc). We find a slope of $-8.2 \pm 0.5$ for the relation between optical magnitude and log rotation speed, in good agreement with Tully-Fisher studies, and a log slope of $1.55 \pm 0.06$ for the HI mass-optical galaxy size relation. Given the homogeneity of the measurements and the completeness of our dataset, the latter outcome suggests that the constancy of the average (hybrid) HI surface density advocated by some authors for the spiral population is a crude approximation.
    The Astrophysical Journal 03/2011; 732. · 6.73 Impact Factor
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    ABSTRACT: We introduce the GALEX Arecibo SDSS Survey (GASS), an on-going large programme that is gathering high quality HI-line spectra using the Arecibo radio telescope for an unbiased sample of ~1000 galaxies with stellar masses greater than 1010^M&sun; and redshifts 0.025
    VizieR Online Data Catalog. 03/2011;

Publication Stats

2k Citations
359.64 Total Impact Points

Institutions

  • 1984–2012
    • Cornell University
      • • Center for Radiophysics and Space Research (CRSR)
      • • Department of Astronomy
      Ithaca, New York, United States
    • University of Puerto Rico at Rio Piedras
      • Department of Physics
      San Juan, San Juan, Puerto Rico
  • 1982–2006
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States
  • 2004
    • National University of Cordoba, Argentina
      Córdoba, Córdoba, Argentina
  • 1993
    • Harvard-Smithsonian Center for Astrophysics
      Cambridge, Massachusetts, United States
    • Cornell College
      Cornell, Wisconsin, United States
  • 1991
    • Yale University
      New Haven, Connecticut, United States
  • 1986
    • National Astronomy and Ionosphere Center
      Arecibo, Arecibo, Puerto Rico
    • Stanford University
      Palo Alto, California, United States
  • 1983
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
  • 1976–1977
    • Indiana University Bloomington
      Bloomington, Indiana, United States