Martha P. Haynes

Cornell University, Итак, New York, United States

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Publications (381)1253.02 Total impact

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    ABSTRACT: We measure the star formation properties of two large samples of galaxies from the SDSS in large-scale cosmic voids on time scales of 10 Myr and 100 Myr, using H$\alpha$ emission line strengths and GALEX FUV fluxes, respectively. The first sample consists of 109,818 optically selected galaxies. We find that void galaxies in this sample have higher specific star formation rates (SSFRs; star formation rates per unit stellar mass) than similar stellar mass galaxies in denser regions. The second sample is a subset of the optically selected sample containing 8070 galaxies with reliable HI detections from ALFALFA. For the full HI detected sample, SSFRs do not vary systematically with large-scale environment. However, investigating only the HI detected dwarf galaxies reveals a trend towards higher SSFRs in voids. Furthermore, we estimate the star formation rate per unit HI mass (known as the star formation efficiency; SFE) of a galaxy, as a function of environment. For the overall HI detected population, we notice no environmental dependence. Limiting the sample to dwarf galaxies again reveals a trend towards higher SFEs in voids. These results suggest that void environments provide a nurturing environment for dwarf galaxy evolution allowing for higher specific star formation rates and efficiencies.
    No preview · Article · Jan 2016
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    ABSTRACT: Leo P is a gas-rich dwarf galaxy with an extremely low gas-phase oxygen abundance (3% solar). The isolated nature of Leo P enables a quantitative measurement of metals lost solely due to star formation feedback. We present an inventory of the oxygen atoms in Leo P based on the gas-phase oxygen abundance measurement, the star formation history, and the chemical enrichment evolution derived from resolved stellar populations. The star formation history also provides the total amount of oxygen produced. Overall, Leo P has retained 5 % of its oxygen; 25% of the retained oxygen is in the stars while 75% is in the gas phase. This is considerably lower than the 20-25% calculated for massive galaxies, supporting the trend for less efficient metal retention for lower mass galaxies. The retention fraction is higher than that calculated for other alpha elements (Mg, Si, Ca) in dSph Milky Way satellites of similar stellar mass and metallicity. Accounting only for the oxygen retained in stars, our results are consistent with those derived for the alpha elements in dSph galaxies. Thus, under the assumption that the dSph galaxies lost the bulk of their gas mass through an environmental process such as tidal stripping, the estimates of retained metal fractions represent underestimates by roughly a factor of four. Because of its isolation, Leo P provides an important datum for the fraction of metals lost as a function of galaxy mass due to star formation.
    Preview · Article · Dec 2015
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    ABSTRACT: We search for environmental dependence of the HI mass function in the ALFALFA 70% catalogue. The catalogue is split into quartiles of environment density based on the projected neighbour density of neighbours found in both SDSS and 2MRS volume limited reference catalogues. We find the Schechter function 'knee' mass to be dependent on environment, with the value of $\log ({M_{*}/\mathrm{M_{\odot}}})$ shifting from $9.81 \pm 0.02$ to $10.00 \pm 0.03$ between the lowest and highest density quartiles. However, this dependence was only observed when defining environment based on the SDSS reference catalogue, not 2MRS. We interpret these results as meaning that the local environment is the dominant cause of the shift in $M_{*}$, and that the larger scales that 2MRS probes (compared to SDSS) are almost irrelevant. In addition, we also use a fixed aperture method to probe environment, and find tentative evidence that HI-deficiency depresses the value of $M_{*}$ in the highest density regions. We find no significant dependence of the low-mass slope on environment in any test, using either method. Tensions between these results and those from the literature, are discussed and alternative explanations are explored.
    No preview · Article · Oct 2015 · Monthly Notices of the Royal Astronomical Society
  • Riccardo Giovanelli · Martha P. Haynes
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    ABSTRACT: We review the results of HI line surveys of extragalactic sources in the local Universe. In the last two decades major efforts have been made in establishing on firm statistical grounds the properties of the HI source population, the two most prominent being the HI Parkes All Sky Survey (HIPASS) and the Arecibo Legacy Fast ALFA survey (ALFALFA). We review the choices of technical parameters in the design and optimization of spectro-photometric "blind" HI surveys, which for the first time produced extensive HI-selected data sets. Particular attention is given to the relationship between optical and HI populations, the differences in their clustering properties and the importance of HI-selected samples in contributing to the understanding of apparent conflicts between observation and theory on the abundance of low mass halos. The last section of this paper provides an overview of currently ongoing and planned surveys which will explore the cosmic evolution of properties of the HI population.
    No preview · Article · Oct 2015 · Astronomy and Astrophysics Review
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    ABSTRACT: We present an analytic model to predict the HI mass contributed by confused sources to a stacked spectrum in a generic HI survey. Based on the ALFALFA correlation function, this model is in agreement with the estimates of confusion present in stacked Parkes telescope data, and was used to predict how confusion will limit stacking in the deepest SKA-precursor HI surveys. Stacking with LADUMA and DINGO UDEEP data will only be mildly impacted by confusion if their target synthesised beam size of 10 arcsec can be achieved. Any beam size significantly above this will result in stacks that contain a mass in confused sources that is comparable to (or greater than) that which is detectable via stacking, at all redshifts. CHILES' 5 arcsec resolution is more than adequate to prevent confusion influencing stacking of its data, throughout its bandpass range. FAST will be the most impeded by confusion, with HI surveys likely becoming heavily confused much beyond z = 0.1. The largest uncertainties in our model are the redshift evolution of the HI density of the Universe and the HI correlation function. However, we argue that the two idealised cases we adopt should bracket the true evolution, and the qualitative conclusions are unchanged regardless of the model choice. The profile shape of the signal due to confusion (in the absence of any detection) was also modelled, revealing that it can take the form of a double Gaussian with a narrow and wide component.
    No preview · Article · Oct 2015 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We present sensitive CO (J = 1 - 0) emission line observations of three metal-poor dwarf irregular galaxies Leo P (Z ~ 3% Z_Solar), Sextans A (Z ~ 7.5% Z_Solar), and Sextans B (Z ~ 7.5% Z_Solar), all obtained with the Combined Array for Millimeter-wave Astronomy (CARMA) interferometer. While no CO emission was detected, the proximity of the three systems allows us to place very stringent (4 sigma) upper limits on the CO luminosity (L_CO) in these metal-poor galaxies. We find the CO luminosities to be L_CO < 2900 K km/s pc^2 for Leo P, L_CO < 12400 K km/s pc^2 for Sextans A, and L_CO < 9700 K km/s pc^2 for Sextans B. Comparison of our results with recent observational estimates of the factor for converting between L_CO and the mass of molecular hydrogen, as well as theoretical models, provides further evidence that either the CO-to-H_2 conversion factor increases sharply as metallicity decreases, or that stars are forming in these three galaxies very efficiently, requiring little molecular hydrogen.
    No preview · Article · Oct 2015 · The Astrophysical Journal
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    ABSTRACT: We measure the r-band galaxy luminosity function (LF) across environments over the redshift range 0<$z$<0.107 using the SDSS. We divide our sample into galaxies residing in large scale voids (void galaxies) and those residing in denser regions (wall galaxies). The best fitting Schechter parameters for void galaxies are: log$\Phi^*$= -3.40$\pm$0.03 log(Mpc$^{-3}$), $M^*$= -19.88$\pm$0.05, and $\alpha$=-1.20$\pm$0.02. For wall galaxies, the best fitting parameters are: log$\Phi^*$=-2.86$\pm$0.02 log(Mpc$^{-3}$), $M^*$=-20.80$\pm$0.03, and $\alpha$=-1.16$\pm$0.01. We find a shift in the characteristic magnitude, $M^*$, towards fainter magnitudes for void galaxies and find no significant difference between the faint-end slopes of the void and wall galaxy LFs. We investigate how low surface brightness selections effects can affect the galaxy LF. To attempt to examine a sample of galaxies that is relatively free of surface brightness selection effects, we compute the optical galaxy LF of galaxies detected by the blind HI survey, ALFALFA. We find that the global LF of the ALFALFA sample is not well fit by a Schechter function, because of the presence of a wide dip in the LF around $M_r$=-18 and an upturn at fainter magnitudes ($\alpha$~-1.47). We compare the HI selected r-band LF to various LFs of optically selected populations to determine where the HI selected optical LF obtains its shape. We find that sample selection plays a large role in determining the shape of the LF.
    Full-text · Article · Aug 2015 · The Astrophysical Journal
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    ABSTRACT: We report on initial results from a campaign to obtain optical imaging of a sample of Ultra Compact High Velocity Clouds (UCHVCs) discovered by the ALFALFA neutral hydrogen (HI) survey. UCHVCs are sources with velocities and sizes consistent with their being low-mass dwarf galaxies in the Local Volume, but without optical counterparts in existing catalogs. We are using the WIYN 3.5-m telescope and pODI camera to image these objects and search for an associated stellar population. In this paper, we present our observational strategy and method for searching for resolved stellar counterparts to the UCHVCs. We combine careful photometric measurements, a color-magnitude filter, and spatial smoothing techniques to search for stellar overdensities in the g- and i-band images. We also run statistical tests to quantify the likelihood that whatever overdensities we find are real and not chance superpositions of sources. We demonstrate the method by applying it to two data sets: WIYN imaging of Leo P, a UCHVC discovered by ALFALFA and subsequently shown to be a low-mass star-forming dwarf galaxy in the Local Volume, and WIYN imaging of AGC198606, an HI cloud identified by ALFALFA that is near in position and velocity to the Local Group dwarf Leo T. Applying the search method to the Leo P data yields an unambiguous detection (>99% confidence) of the galaxy's stellar population. Applying our method to the AGC198606 imaging yields a possible detection (92% confidence) of an optical counterpart located ~2.5 arc minutes away from the centroid of AGC198606's HI distribution and within the HI disk. We use the optical data to estimate a distance to the stellar counterpart between 373 and 393 kpc, with an absolute magnitude M_i = -4.67+/-0.09. Combining the WIYN data with our previous estimate of the HI mass of AGC198606 from WSRT imaging yields an HI-to-stellar mass ratio of ~45-110.
    Preview · Article · Aug 2015 · The Astrophysical Journal
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    ABSTRACT: We present Arecibo, GBT, VLA and WIYN/pODI observations of the ALFALFA source AGC 226067. Originally identified as an ultra-compact high velocity cloud and candidate Local Group galaxy, AGC 226067 is spatially and kinematically coincident with the Virgo cluster, and the identification by multiple groups of an optical counterpart with no resolved stars supports the interpretation that this systems lies at the Virgo distance (D=17 Mpc). The combined observations reveal that the system consists of multiple components: a central HI source associated with the optical counterpart (AGC 226067), a smaller HI-only component (AGC 229490), a second optical component (AGC 229491), and extended low surface brightness HI. Only ~1/4 of the single-dish HI emission is associated with AGC 226067; as a result, we find M_HI/L_g ~ 6 Msun/Lsun, which is lower than previous work. At D=17 Mpc, AGC 226067 has an HI mass of 1.5 x 10^7 Msun and L_g = 2.4 x 10^6 Lsun, AGC 229490 (the HI-only component) has M_HI = 3.6 x 10^6 Msun, and AGC 229491 (the second optical component) has L_g = 3.6 x 10^5 Lsun. The nature of this system of three sources is uncertain: AGC 226067 and AGC 229490 may be connected by an HI bridge, and AGC 229490 and AGC 229491 are separated by only 0.5'. The current data do not resolve the HI in AGC 229490 and its origin is unclear. We discuss possible scenarios for this system of objects: an interacting system of dwarf galaxies, accretion of material onto AGC 226067, or stripping of material from AGC 226067.
    Preview · Article · Jul 2015 · Astronomy and Astrophysics
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    ABSTRACT: Leo P is a low-luminosity dwarf galaxy discovered through the blind HI Arecibo Legacy Fast ALFA (ALFALFA) survey. The HI and follow-up optical observations have shown that Leo P is a gas-rich dwarf galaxy with active star formation, an underlying older population, and an extremely low oxygen abundance. We have obtained optical imaging from the Hubble Space Telescope to study the evolution of Leo P. We refine the distance measurement to Leo~P to be 1.62+/-0.15 Mpc, based on the luminosity of the horizontal branch stars and 10 newly identified RR Lyrae candidates. This places the galaxy at the edge of the Local Group, ~0.4 Mpc from the loose association of dwarfs that includes Sextans A, Sextans B, Antlia, and NGC 3109. The star responsible for ionizing the HII region is most likely an O7V or O8V spectral type, with a stellar mass >25 Msun. The presence of this star provides observational evidence that massive stars at the upper-end of the initial mass function are capable of being formed at star formation rates as low as ~10^-5 Msun/yr. The best-fitting star formation history derived from the resolved stellar populations of Leo P using the latest PARSEC models shows a relatively constant star formation rate over the lifetime of the galaxy. The modeled luminosity characteristics of Leo P at early times are consistent with low-luminosity dSph Milky Way satellites, suggesting that Leo P is what a low-mass dSph would look like if it evolved in isolation and retained its gas. Despite the very low mass of Leo P, the imprint of reionization on its star formation history is subtle at best, and consistent with being totally negligible. The isolation of Leo P, and the total quenching of star formation of Milky Way satellites of similar mass, implies that local environment dominates the quenching of the Milky Way satellites.
    Full-text · Article · Jun 2015 · The Astrophysical Journal
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    ABSTRACT: HI in galaxies traces the fuel for future star formation and reveals the effects of feedback on neutral gas. Using a statistically uniform, HI-selected sample of 565 galaxies from the ALFALFA H-alpha survey, we explore HI properties as a function of star formation activity. ALFALFA H-alpha provides R-band and H-alpha imaging for a volume-limited subset of the 21-cm ALFALFA survey. We identify eight starbursts based on H-alpha equivalent width and six with enhanced star formation relative to the main sequence. Both starbursts and non-starbursts have similar HI to stellar mass ratios (MHI/M*), which suggests that feedback is not depleting the starbursts' HI. Consequently, the starbursts do have shorter HI depletion times (t_dep), implying more efficient HI-to-H2 conversion. While major mergers likely drive this enhanced efficiency in some starbursts, the lowest mass starbursts may experience periodic bursts, consistent with enhanced scatter in t_dep at low M*. Two starbursts appear to be pre-coalescence mergers; their elevated MHI/M* suggest that HI-to-H2 conversion is still ongoing at this stage. By comparing with the GASS sample, we find that t_dep anti-correlates with stellar surface density for disks, while spheroids show no such trend. Among early-type galaxies, t_dep does not correlate with bulge-to-disk ratio; instead, the gas distribution may determine the star formation efficiency. Finally, the weak connection between galaxies' specific star formation rates and MHI/M* contrasts with the well-known correlation between MHI/M* and color. We show that dust extinction can explain the HI-color trend, which may arise from the relationship between M*, MHI, and metallicity.
    Full-text · Article · Jun 2015 · The Astrophysical Journal
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    ABSTRACT: We revisit the main H i-to-stellar mass ratio (gas fraction) scaling relations, taking advantage of the H i spectral stacking technique to understand the dependence of gas content on the structural and star formation properties of nearby galaxies. This work uses a volume-limited, multiwavelength sample of ∼25 000 galaxies, selected according to stellar mass (109 M⊙ ≤ M⋆ ≤ 1011.5 M⊙) and redshift (0.02 ≤ z ≤ 0.05) from the Sloan Digital Sky Survey, and with H i data from the Arecibo Legacy Fast ALFA survey. We bin according to multiple parameters of galaxies spanning the full gas-poor to -rich regime in order to disentangle the dominance of different components and processes in influencing gas content. For the first time, we show that the scaling relations of gas fraction with stellar mass and stellar surface density are primarily driven by a combination of the underlying galaxy bimodality in specific star formation rate and the integrated Kennicutt–Schmidt law. Finally, we produce tentative evidence that the time-scales of H i depletion are dependent upon galaxy mass and structure, at fixed specific star formation rate.
    Preview · Article · Jun 2015 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: A growing body of evidence indicates that the star formation rate per unit stellar mass (sSFR) decreases with increasing mass in normal "main-sequence" star forming galaxies. Many processes have been advocated as responsible for such a trend (also known as mass quenching), e.g., feedback from active galactic nuclei (AGNs), and the formation of classical bulges. We determine a refined star formation versus stellar mass relation in the local Universe. To this aim we use the Halpha narrow-band imaging follow-up survey (Halpha3) of field galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) in the Coma and Local superclusters. By complementing this local determination with high-redshift measurements from the literature, we reconstruct the star formation history of main-sequence galaxies as a function of stellar mass from the present epoch up to z=3. In agreement with previous studies, our analysis shows that quenching mechanisms occur above a threshold stellar mass M_knee that evolves with redshift as propto (1+z)^{2}. Moreover, visual morphological classification of individual objects in our local sample reveals a sharp increase in the fraction of visually-classified strong bars with mass, hinting that strong bars may contribute to the observed downturn in the sSFR above M_knee. We test this hypothesis using a simple but physically-motivated numerical model for bar formation, finding that strong bars can rapidly quench star formation in the central few kpc of field galaxies. We conclude that strong bars contribute significantly to the red colors observed in the inner parts of massive galaxies, although additional mechanisms are likely required to quench the star formation in the outer regions of massive spiral galaxies. Intriguingly, when we extrapolate our model to higher redshifts, we successfully recover the observed redshift evolution for M_knee.
    Preview · Article · May 2015 · Astronomy and Astrophysics
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    ABSTRACT: Neutral hydrogen represents the major observable baryonic constituent of galaxies that fuels the formation of stars through the transformation in molecular hydrogen. The emission of the hydrogen recombination line Halpha is the most direct tracer of the process that transforms gas (fuel) into stars. We continue to present Halpha3 (acronym for Halpha-alpha-alpha), an extensive Halpha+[NII] narrow-band imaging campaign of galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA), using the instrumentation available at the San Pedro Martir observatory (Mexico). In only four years since 2011 we were able to complete in 48 nights the Halpha imaging observations of 724 galaxies in the region of the Coma supercluster 10^h < R.A. <16^h; 24^o < Dec. <28^o and 3900<cz<9000 kms^{-1}. Of these, 603 are selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) and constitute a 97% complete sample. They provide for the first time a complete census of the massive star formation properties of local gas-rich galaxies belonging to different environments (cluster vs filaments), morphological type (spirals vs dwarf Irr), over a wide range of stellar mass (10^{8}-10^{11.5} Modot) in the Coma Supercluster. The present Paper V provides the Halpha data and the derived star formation rates for the observed galaxies.
    Full-text · Article · May 2015 · Astronomy and Astrophysics
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    ABSTRACT: We present a comprehensive model to predict the rate of spectroscopic confusion in HI surveys, and demonstrate good agreement with the observable confusion in existing surveys. Generically the action of confusion on the HI mass function was found to be a suppression of the number count of sources below the `knee', and an enhancement above it. This results in a bias, whereby the `knee' mass is increased and the faint end slope is steepened. For ALFALFA and HIPASS we find that the maximum impact this bias can have on the Schechter fit parameters is similar in magnitude to the published random errors. On the other hand, the impact of confusion on the HI mass functions of upcoming medium depth interferometric surveys, will be below the level of the random errors. In addition, we find that previous estimates of the number of detections for upcoming surveys with SKA-precursor telescopes may have been too optimistic, as the framework implemented here results in number counts between 60% and 75% of those previously predicted, while accurately reproducing the counts of existing surveys. Finally, we argue that any future single dish, wide area surveys of HI galaxies would be best suited to focus on deep observations of the local Universe (z < 0.05), as confusion may prevent them from being competitive with interferometric surveys at higher redshift, while their lower angular resolution allows their completeness to be more easily calibrated for nearby extended sources.
    Preview · Article · Feb 2015 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We report the discovery and follow-up observations of a system of three objects identified by the ALFALFA extragalactic HI survey, cataloged as (almost) dark extragalactic sources, i.e., extragalactic HI detections with no discernible counterpart in publicly available, wide-field, imaging surveys. We have obtained deep optical imaging with WIYN pODI and HI synthesis maps with WSRT of the HI1232+20 system. The source with the highest HI flux has a newly discovered ultra-low surface brightness (LSB) optical counterpart associated with it, while the other two sources have no detected optical counterparts in our images. Our optical observations show that the detected LSB optical counterpart has a peak surface brightness of ~26.4 mag/arcsec^2 in g', which is exceptionally faint. This source (AGC 229385) has the largest accurately measured HI mass-to-light ratio of an isolated object: MHI/Lg'=46 Msun/Lsun, and has an HI mass of 7.2*10^8 Msun. The other two HI sources (with HI masses 2.0*10^8 and 1.2*10^8 Msun) without optical counterparts have upper limit surface brightnesses of 27.9 and 27.8 mag/arcsec^2 in g', and lower limits on their gas mass-to-light ratio of MHI/Lg'>57 and >31 Msun/Lsun. This system lies relatively close in projection to the Virgo Cluster, but velocity flow models indicate that it is located at ~25 Mpc, substantially beyond Virgo. The system appears to be quite isolated, with no known object closer than 500 kpc. These HI sources may represent both sides of the threshold between "dark" star-less galaxies and galaxies with stellar populations. We discuss a variety of possible formation scenarios for the HI1232+20 system.
    Preview · Article · Feb 2015 · The Astrophysical Journal
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    ABSTRACT: The Survey of HI in Extremely Low-mass Dwarfs (SHIELD) is an on-going multi-wavelength program to characterize the gas, star formation, and evolution in gas-rich, very low-mass galaxies that populate the faint end of the galaxy luminosity function. The galaxies were selected from the first ~10% of the HI ALFALFA survey based on their low HI mass and low baryonic mass. Here, we measure the star-formation properties from optically resolved stellar populations for 12 galaxies using a color-magnitude diagram fitting technique. We derive lifetime average star-formation rates (SFRs), recent SFRs, stellar masses, and gas fractions. Overall, the recent SFRs are comparable to the lifetime SFRs with mean birthrate parameter of 1.4, with a surprisingly narrow standard deviation of 0.7. Two galaxies are classified as dwarf transition galaxies (dTrans). These dTrans systems have star-formation and gas properties consistent with the rest of the sample, in agreement with previous results that some dTrans galaxies may simply be low-luminosity dIrrs. We do not find a correlation between the recent star-formation activity and the distance to the nearest neighboring galaxy, suggesting that the star-formation process is not driven by gravitational interactions, but regulated internally. Further, we find a broadening in the star-formation and gas properties (i.e., specific SFRs, stellar masses, and gas fractions) compared to the generally tight correlation found in more massive galaxies. Overall, the star-formation and gas properties indicate these very low-mass galaxies host a fluctuating, non-deterministic, and inefficient star-formation process.
    Preview · Article · Jan 2015 · The Astrophysical Journal
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    ABSTRACT: We present VLA HI spectral line imaging of 5 sources discovered by ALFALFA. These targets are drawn from a larger sample of systems that were not uniquely identified with optical counterparts during ALFALFA processing, and as such have unusually high HI mass to light ratios. These candidate "Almost Dark" objects fall into 4 categories: 1) objects with nearby HI neighbors that are likely of tidal origin; 2) objects that appear to be part of a system of multiple HI sources, but which may not be tidal in origin; 3) objects isolated from nearby ALFALFA HI detections, but located near a gas-poor early-type galaxy; 4) apparently isolated sources, with no object of coincident redshift within ~400 kpc. Roughly 75% of the 200 objects without identified counterparts in the $\alpha$.40 database (Haynes et al. 2011) fall into category 1. This pilot sample contains the first five sources observed as part of a larger effort to characterize HI sources with no readily identifiable optical counterpart at single dish resolution. These objects span a range of HI mass [7.41 < log(M$_{\rm HI}$) < 9.51] and HI mass to B-band luminosity ratios (3 < M$_{\rm HI}$/L$_{\rm B}$ < 9). We compare the HI total intensity and velocity fields to SDSS optical imaging and to archival GALEX UV imaging. Four of the sources with uncertain or no optical counterpart in the ALFALFA data are identified with low surface brightness optical counterparts in SDSS imaging when compared with VLA HI intensity maps, and appear to be galaxies with clear signs of ordered rotation. One source (AGC 208602) is likely tidal in nature. We find no "dark galaxies" in this limited sample. The present observations reveal complex sources with suppressed star formation, highlighting both the observational difficulties and the necessity of synthesis follow-up observations to understand these extreme objects. (abridged)
    Full-text · Article · Dec 2014 · The Astronomical Journal
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    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.
    Preview · Article · Nov 2014 · Astronomy and Astrophysics
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    ABSTRACT: We present first results of the study of a set of exceptional H I sources identified in the 40% ALFALFA extragalactic H I survey catalog alpha.40 as both being H I massive (M-H I > 10(10) M-circle dot) and having high gas fractions for their stellar masses: the HIghMass galaxy sample. We analyze UV- and optical-broadband and H alpha images to understand the nature of their relatively underluminous disks in optical and to test whether their high gas fractions can be tracked to higher dark matter halo spin parameters or late gas accretion. Estimates of their star formation rates (SFRs) based on spectral energy distribution fitting agree within uncertainties with the Ha luminosity inferred current massive SFRs. The H II region luminosity functions, parameterized as dN/d log L alpha L-alpha, have standard slopes at the luminous end (alpha similar to -1). The global SFRs demonstrate that the HIghMass galaxies exhibit active ongoing star formation (SF) with moderate SF efficiency but, relative to normal spirals, a lower integrated SFR in the past. Because the SF activity in these systems is spread throughout their extended disks, they have overall lower SFR surface densities and lower surface brightness in the optical bands. Relative to normal disk galaxies, the majority of HIghMass galaxies have higher H alpha equivalent widths and are bluer in their outer disks, implying an inside-out disk growth scenario. Downbending double exponential disks are more frequent than upbending disks among the gas-rich galaxies, suggesting that SF thresholds exist in the downbending disks, probably as a result of concentrated gas distribution.
    Preview · Article · Sep 2014 · The Astrophysical Journal

Publication Stats

10k Citations
1,253.02 Total Impact Points

Institutions

  • 1985-2015
    • Cornell University
      • • Center for Radiophysics and Space Research (CRSR)
      • • Department of Astronomy
      Итак, New York, United States
  • 2004
    • University of Cambridge
      • Institute of Astronomy
      Cambridge, England, United Kingdom
  • 1993-1999
    • Cornell College
      Cornell, Wisconsin, United States
  • 1998
    • Wesleyan University
      • Department of Astronomy
      Middletown, Connecticut, United States
    • New Mexico Institute of Mining and Technology
      • Department of Physics
      Socorro, New Mexico, United States
  • 1988
    • Harvard-Smithsonian Center for Astrophysics
      Cambridge, Massachusetts, United States
  • 1986-1988
    • National Astronomy and Ionosphere Center
      ARE, Arecibo, Puerto Rico
  • 1984
    • University of Puerto Rico at Rio Piedras
      • Department of Physics
      San Juan, San Juan, Puerto Rico
  • 1983
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
  • 1982-1983
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States
  • 1981-1983
    • University of Oklahoma
      Norman, Oklahoma, United States
  • 1979
    • University of Bologna
      Bolonia, Emilia-Romagna, Italy
  • 1976-1979
    • Indiana University Bloomington
      • Department of Astronomy
      Bloomington, Indiana, United States