M. P. Haynes

Loyola University Maryland, Baltimore, Maryland, United States

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Publications (357)1210.59 Total impact

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    ABSTRACT: We measure the HI mass function (HIMF) and velocity width function (WF) across environments over a range of masses $7.2<\log(M_{HI}/M_{\odot})<10.8$, and profile widths $1.3\log(km/s)<\log(W)<2.9\log(km/s)$, using a catalog of ~7,300 HI-selected galaxies from the ALFALFA Survey, located in the region of sky where ALFALFA and SDSS (Data Release 7) North overlap. We divide our galaxy sample into those that reside in large-scale voids (void galaxies) and those that live in denser regions (wall galaxies). We find the void HIMF to be well fit by a Schechter function with normalization $\Phi^*=(1.37\pm0.1)\times10^{-2} h^3Mpc^{-3}$, characteristic mass $\log(M^*/M_{\odot})+2\log h_{70}=9.86\pm0.02$, and low-mass-end slope $\alpha=-1.29\pm0.02$. Similarly, for wall galaxies, we find best-fitting parameters $\Phi^*=(1.82\pm0.03)\times10^{-2} h^3Mpc^{-3}$, $\log(M^*/M_{\odot})+2\log h_{70}=10.00\pm0.01$, and $\alpha=-1.35\pm0.01$. We conclude that void galaxies typically have slightly lower HI masses than their non-void counterparts, which is in agreement with the dark matter halo mass function shift in voids assuming a simple relationship between DM mass and HI mass. We also find that the low-mass slope of the void HIMF is similar to that of the wall HIMF suggesting that there is either no excess of low-mass galaxies in voids or there is an abundance of intermediate HI mass galaxies. We fit a modified Schechter function to the ALFALFA void WF and determine its best-fitting parameters to be $\Phi^*=0.21\pm0.1 h^3Mpc^{-3}$, $\log(W^*)=2.13\pm0.3$, $\alpha=0.52\pm0.5$ and high-width slope $\beta=1.3\pm0.4$. For wall galaxies, the WF parameters are: $\Phi^*=0.022\pm0.009 h^3Mpc^{-3}$, $\log(W^*)=2.62\pm0.5$, $\alpha=-0.64\pm0.2$ and $\beta=3.58\pm1.5$. Because of large uncertainties on the void and wall width functions, we cannot conclude whether the WF is dependent on the environment.
    08/2014;
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    ABSTRACT: We present first results of the study of a set of exceptional HI sources identified in the 40% ALFALFA extragalactic HI survey catalog alpha.40 as being both HI massive (M_HI > 10^10 Msun) and having high gas fractions for their stellar masses: the HIghMass galaxy sample. We analyze UV- and optical-broadband and Halpha 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 SED-fitting agree within uncertainties with the Halpha luminosity inferred SFRs. The HII region luminosity functions have standard slopes at the luminous end. 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 Halpha 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.
    07/2014;
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    ABSTRACT: We use the Arecibo Legacy Fast ALFA (ALFALFA) 21cm survey to measure the number density of galaxies as a function of their rotational velocity, Vrot,HI (as inferred from the width of their 21cm emission line). Based on the measured velocity function we statistically connect galaxies with their host halos, via abundance matching. In a LCDM cosmology, low-velocity galaxies are expected to be hosted by halos that are significantly more massive than indicated by the measured galactic velocity; allowing lower mass halos to host ALFALFA galaxies would result in a vast overestimate of their number counts. We then seek observational verification of this predicted trend, by analyzing the kinematics of a literature sample of field dwarf galaxies. We find that galaxies with Vrot,HI<25 km/s are kinematically incompatible with their predicted LCDM host halos, in the sense that hosts are too massive to be accommodated within the measured galactic rotation curves. This issue is analogous to the "too big to fail" problem faced by the bright satellites of the Milky Way, but here it concerns extreme dwarf galaxies in the field. Consequently, solutions based on satellite-specific processes are not applicable in this context. Our result confirms the findings of previous studies based on optical survey data, and addresses a number of observational systematics present in these works. Furthermore, we point out the assumptions and uncertainties that could strongly affect our conclusions. We show that the two most important among them, namely baryonic effects on the abundances and rotation curves of halos, do not seem capable of resolving the reported discrepancy.
    07/2014;
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    ABSTRACT: We present resolved HI observations of two galaxies, UGC 9037 and UGC 12506, members of a rare subset of galaxies detected by the ALFALFA extragalactic HI survey characterized by high HI mass and high gas fraction for their stellar masses. Both of these galaxies have M$_*>10^{10}$ M$_\odot$ and M$_\text{HI}>$ M$_*$, as well as typical star formation rates for their stellar masses. How can such galaxies have avoided consuming their massive gas reservoirs? From gas kinematics, stability, star formation, and dark matter distributions of the two galaxies, we infer two radically different histories. UGC 9037 has high central HI surface density ($>10$ M$_\odot$ pc$^{-2}$). Its gas at most radii appears to be marginally unstable with non-circular flows across the disk. These properties are consistent with UGC 9037 having recently acquired its gas and that it will soon undergo major star formation. UGC 12506 has low surface densities of HI, and its gas is stable over most of the disk. We predict its gas to be HI-dominated at all except the smallest radii. We claim a very high dark matter halo spin parameter for UGC 12506 ($\lambda=0.15$), suggesting that its gas is older, and has never undergone a period of star formation significant enough to consume the bulk of its gas.
    07/2014;
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    ABSTRACT: We present GMRT HI observations and deep CFHT MegaCam optical images of the gas-rich interacting galaxy group NGC 871/NGC 876/NGC 877 (hereafter NGC 871/6/7). Our high-resolution data sets provide a census of the HI and stellar properties of the detected gas-rich group members. In addition to a handful of spiral, irregular and dwarf galaxies, this group harbours an intriguing HI feature, AGC 749170, that has a gas mass of ~10^9.3 M_sol, a dynamical-to-gas mass ratio of ~1 (assuming the cloud is rotating and in dynamical equilibrium) and no optical counterpart in previous imaging. Our observations have revealed a faint feature in the CFHT g'- and r'-bands; if it is physically associated with AGC 749170, the latter has M/L_g > 1000 M_sol/L_sol as well as a higher metallicity (estimated using photometric colours) and a significantly younger stellar population than the other low-mass gas-rich group members. These properties, as well as its spectral and spatial location with respect to its suspected parent galaxies, strongly indicate a tidal origin for AGC 749170. Overall, the HI properties of AGC 749170 resemble those of other optically dark/dim clouds that have been found in groups. These clouds could represent a class of relatively long-lived HI-rich tidal remnants that survive in intermediate-density environments.
    07/2014;
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    ABSTRACT: We present new HI spectral line imaging of the extremely metal-poor, star-forming dwarf irregular galaxy Leo P. Our HI images probe the global neutral gas properties and the local conditions of the interstellar medium (ISM). The HI morphology is slightly elongated along the optical major-axis. We do not find obvious signatures of interaction or infalling gas at large spatial scales. The neutral gas disk shows obvious rotation, although the velocity dispersion is comparable to the rotation velocity. The rotation amplitude is estimated to be V_c = 15 +/- 5 km/s. Within the HI radius probed by these observations, the mass ratio of gas to stars is roughly 2:1, while the ratio of the total mass to the baryonic mass is ~15:1. We use this information to place Leo P on the baryonic Tully-Fisher relation, testing the baryonic content of cosmic structures in a sparsely populated portion of parameter space that has hitherto been occupied primarily by dwarf spheroidal galaxies. We detect the signature of two temperature components in the neutral ISM of Leo P; the cold and warm components have characteristic velocity widths of 4.2 +/- 0.9 km/s and 10.1 +/- 1.2 km/s, corresponding to kinetic temperatures of ~1100 K and ~6200 K, respectively. The cold HI component is unresolved at a physical resolution of 200 pc. The highest HI surface densities are observed in close physical proximity to the single HII region. A comparison of the neutral gas properties of Leo P with other extremely metal-deficient (XMD) galaxies reveals that Leo P has the lowest neutral gas mass of any known XMD, and that the dynamical mass of Leo P is more than two orders of magnitude smaller than any known XMD with comparable metallicity.
    The Astronomical Journal 04/2014; 148(2). · 4.97 Impact Factor
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    ABSTRACT: The Survey of H I in Extremely Low-mass Dwarf (SHIELD) galaxies is an ongoing multi-wavelength program to characterize the gas, star formation, and evolution in gas-rich, very low-mass galaxies. The galaxies were selected from the first ~10% of the H I Arecibo Legacy Fast ALFA (ALFALFA) survey based on their inferred low H I mass and low baryonic mass, and all systems have recent star formation. Thus, the SHIELD sample probes the faint end of the galaxy luminosity function for star-forming galaxies. Here, we measure the distances to the 12 SHIELD galaxies to be between 5 and 12 Mpc by applying the tip of the red giant method to the resolved stellar populations imaged by the Hubble Space Telescope. Based on these distances, the H I masses in the sample range from 4 × 106 to 6 × 107 M ☉, with a median H I mass of 1 × 107 M ☉. The tip of the red giant branch distances are up to 73% farther than flow-model estimates in the ALFALFA catalog. Because of the relatively large uncertainties of flow-model distances, we are biased toward selecting galaxies from the ALFALFA catalog where the flow model underestimates the true distances. The measured distances allow for an assessment of the native environments around the sample members. Five of the galaxies are part of the NGC 672 and NGC 784 groups, which together constitute a single structure. One galaxy is part of a larger linear ensemble of nine systems that stretches 1.6 Mpc from end to end. Three galaxies reside in regions with 1-9 neighbors, and four galaxies are truly isolated with no known system identified within a radius of 1 Mpc.Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
    03/2014; 785(1).
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    ABSTRACT: The Survey of HI in Extremely Low-mass Dwarf galaxies (SHIELD) is an on-going multi-wavelength program to characterize the gas, star formation, and evolution in gas-rich, very low-mass galaxies. The galaxies were selected from the first ~10% of the HI ALFALFA survey based on their inferred low HI mass and low baryonic mass, and all systems have recent star formation. Thus, the SHIELD sample probes the faint end of the galaxy luminosity function for star-forming galaxies. Here, we measure the distances to the 12 SHIELD galaxies to be between 5-12 Mpc by applying the tip of the red giant method to the resolved stellar populations imaged by the Hubble Space Telescope. Based on these distances, the HI masses in the sample range from $4\times10^6$ to $6\times10^7$ M$_{\odot}$, with a median HI mass of $1\times10^7$ M$_{\odot}$. The TRGB distances are up to 73% farther than flow-model estimates in the ALFALFA catalog. Because of the relatively large uncertainties of flow model distances, we are biased towards selecting galaxies from the ALFALFA catalog where the flow model underestimates the true distances. The measured distances allow for an assessment of the native environments around the sample members. Five of the galaxies are part of the NGC 672 and NGC 784 groups, which together constitute a single structure. One galaxy is part of a larger linear ensemble of 9 systems that stretches 1.6 Mpc from end to end. Two galaxies reside in regions with 1-4 neighbors, and four galaxies are truly isolated with no known system identified within a radius of 1 Mpc.
    02/2014;
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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 4x107 M⊙, detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. Here we present new structural parameters of the SHIELD galaxies determined from Hubble Space Telescope (HST) images. The primary goal is an accurate determination of the optical surface brightness of each galaxy. We designed a custom IDL program, called CleanGalaxy, that allows accurate removal of foreground and background contaminants, and then automatically fits elliptical surface brightness contours as a function of galactocentric radius. The extracted surface brightness profiles are parameterized using standard scaling laws. We compare these structural parameters for all members of the SHIELD galaxies and present cumulative surface brightness measurements of each system. Support for this work was provided by NASA through grant GO-12658 from the Space Telescope Institute, which is operated by Aura, Inc., under NASA contract NAS5-26555. JMC is supported by NSF grant AST-1211683. E. D. S. is grateful for partial support from the University of Minnesota.
    01/2014;
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    ABSTRACT: Dark galaxies are galaxies that have few stars and are made mostly of dense gas. These objects are expected to be difficult to detect with optical telescopes. Dark galaxies are thought to exist possibly associated to tidal interactions between galaxies, or they might represent an early stage in the process of galaxy formation. The prototype for dark galaxies is the southwestern component of HI 1225+01 (Chengalur et al. 1995, AJ 109, 2415) with an HI mass of 8*10^8M⊙ circular velocity ~34 km/s. The Arecibo Legacy Fast ALFA extragalactic survey (ALFALFA) is a blind HI survey completed in 2012. One of the scientific objectives of ALFALFA was the possible detection of HI tidal remnants (Giovanelli et al. 2005, AJ 130, 2598). Less than 2% of the total extragalactic population of the α.40 Source Catalog from ALFALFA are classified as dark HI sources (Haynes et al. 2011, AJ. 142,170). As part of our participation of the Undergraduate ALFALFA Team we present an analysis of the infrared data from WISE of a sample of the most extreme high M_HI/ almost dark galaxies being studied by the ALFALFA team. Some of these objects have no detectable optical emission in SDSS images, while others may be associated with very faint, low luminosity stellar counterparts. For HI 1225+01, Matsuoka et al (2012, AJ 144,159) obtained an R band image of the NE clump of this object, and also found emission in the Spitzer IRAC bands of 3.6μm and 4.5μm among others. No emission was found In the SW component. We present our findings of the emission at 3.4, 4.6 and 12μm from WISE of a region centered on the almost dark galaxies. This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We gratefully acknowledge the support from the NSF grant AST-1211005 for this project.
    01/2014;
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    ABSTRACT: We present sensitive observations in the CO J = 1 → 0 emission line of the metal-poor dwarf irregular galaxies Sextans A, Sextans B, and Leo P, all obtained with the CARMA interferometer. While no confirmed detections of CO emission were found, the proximity of the three systems allows us to place very stringent upper limits on the CO luminosity in metal poor galaxies. We find the CO luminosities to be LCO < 2270 K km/s pc2 for Leo P, LCO < 6490 K km/s pc2 for Sextans B, and LCO < 8550 K km/s pc2 for Sextans A. These are among the most sensitive CO upper limits in metal poor galaxies to date. Comparing the star formation rate to our CO upper limit provides evidence that either the CO to H2 conversion factor increases sharply as metallicity decreases, or stars are forming in these three galaxies very efficiently, requiring little molecular hydrogen. The Cornell ALFALFA team is supported by NSF AST-1107390 and by the Brinson Foundation. The Undergraduate ALFALFA Team is supported by NSF grant AST-1211005. JMC is supported by NSF grant AST-1211683.
    01/2014;
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    ABSTRACT: We present new pilot VLA HI spectral line imaging of five enigmatic sources discovered by the ALFALFA extragalactic survey. These five targets are drawn from a larger sample of ‘Almost Dark’ systems that have unusually high hydrogen mass to light ratios. The candidate ‘Almost Dark’ systems fall into four broad categories: 1) systems that lack a stellar counterpart in moderate-depth optical imaging; 2) systems with very low surface brightness stellar populations; 3) systems with multiple possible optical counterparts; 4) systems with HI in the vicinity of, but offset from, early-type galaxies. The five sources presented here (AGC193953, AGC208602, AGC208399, AGC226178, and AGC233638) include at least one source in each broad category. HI emission is detected in all five systems. We compare the resulting HI total intensity and coarse velocity fields to optical imaging drawn from the Sloan Digitized Sky Survey. These pilot observations set the stage for a major follow-up HI observing campaign that is now underway with the Westerbork Synthesis Radio Telescope. The Cornell ALFALFA team is supported by NSF AST-1107390 and by the Brinson Foundation. The Undergraduate ALFALFA Team is supported by NSF grant AST-1211005. JMC is supported by NSF grant AST-1211683.
    01/2014;
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    ABSTRACT: The interplay of gas inflows, star formation, and feedback drives galaxy evolution, and starburst galaxies provide important laboratories for probing these processes at their most extreme. With two samples of low-redshift starburst galaxies, we examine the conversion of neutral gas into stars and the subsequent effects of stellar feedback on the neutral interstellar medium (ISM). The ALFALFA Hα survey represents a complete, volume-limited sample of HI-selected galaxies with 21 cm spectra and Hα and R-band imaging. By contrasting the starburst galaxies with the rest of the gas-rich galaxy population, we investigate the roles of galaxy morphology, HI kinematics, and the atomic gas supply in triggering extreme levels of star formation. Both an elevated HI gas supply and an external disturbance are necessary to drive the starbursts. While neutral gas may fuel a starburst, it may also increase starbursts' optical depths and hinder the transport of ionizing radiation. In contrast to the expectations for high-redshift star-forming galaxies, neutral gas appears to effectively bar the escape of ionizing radiation in most low-redshift starbursts. To evaluate the impact of radiative feedback in extreme starbursts, we analyze optical spectra of the Green Pea galaxies, a low-redshift sample selected by their intense [O III] λ5007 emission and compact sizes. We use nebular photoionization and stellar population models to constrain the Peas' burst ages, ionizing sources, and optical depths and find that the Peas are likely optically thin to Lyman continuum (LyC) radiation. These young starbursts still generate substantial ionizing radiation, while recent supernovae may have carved holes in the ISM that enhance LyC photon escape into the intergalactic medium. While the ALFALFA survey demonstrates the role of external processes in triggering starbursts, the Green Peas show that starbursts' radiation can escape to affect their external environment.
    01/2014;
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    ABSTRACT: The paucity of low mass galaxies in the Universe is a long-standing problem. 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. Seven of these systems have been observed with WSRT to enable higher spatial resolution 40-60") studies of the HI distribution. The HI morphology revealed by the WSRT data offers clues to the environment of the UCHVCs, and velocity fields allow the underlying mass distribution to be constrained. The Cornell ALFALFA team is supported by NSF AST-1107390 and by the Brinson Foundation. JMC is supported by NSF grant AST-1211683.
    01/2014;
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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 both active star formation and an underlying older population, as well as an extremely low oxygen abundance. Here, we measure the distance to Leo P by applying the tip of the red giant branch (TRGB) distance method to photometry of the resolved stellar population from new Large Binocular Telescope (LBT) V and I band imaging. We measure a distance modulus of 26.19 (+0.17/-0.50) mag corresponding to a distance of 1.72 (+0.14/-0.40) Mpc. Although our photometry reaches 3 magnitudes below the TRGB, the sparseness of the red giant branch (RGB) yields higher uncertainties on the lower limit of the distance. Leo P is outside the Local Group with a distance and velocity consistent with the local Hubble flow. While located in a very low-density environment, Leo P lies within ~0.5 Mpc of a loose association of dwarf galaxies which include NGC 3109, Antlia, Sextans A, and Sextans B, and 1.1 Mpc away from its next nearest neighbor, Leo A. Leo P is one of the lowest metallicity star-forming galaxies known in the nearby universe, comparable in metallicity to I Zw 18 and DDO 68, but with stellar characteristics similar to dwarf spheriodals (dSphs) in the Local Volume such as Carina, Sextans, and Leo II. Given its physical properties and isolation, Leo P may provide an evolutionary link between gas-rich dwarf irregular galaxies and dSphs that have fallen into a Local Group environment and been stripped of their gas.
    The Astronomical Journal 09/2013; 146(6). · 4.97 Impact Factor
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    ABSTRACT: We use a sample of ~6000 galaxies detected by the Arecibo Legacy Fast ALFA (ALFALFA) 21cm survey, to measure the clustering properties of HI-selected galaxies. We find no convincing evidence for a dependence of clustering on the galactic atomic hydrogen (HI) mass, over the range M_HI ~ 10^{8.5} - 10^{10.5} M_sun. We show that previously reported results of weaker clustering for low-HI mass galaxies are probably due to finite-volume effects. In addition, we compare the clustering of ALFALFA galaxies with optically selected samples drawn from the Sloan Digital Sky Survey (SDSS). We find that HI-selected galaxies cluster more weakly than even relatively optically faint galaxies, when no color selection is applied. Conversely, when SDSS galaxies are split based on their color, we find that the correlation function of blue optical galaxies is practically indistinguishable from that of HI-selected galaxies. At the same time, SDSS galaxies with red colors are found to cluster significantly more than HI-selected galaxies, a fact that is evident in both the projected as well as the full two-dimensional correlation function. A cross-correlation analysis further reveals that gas-rich galaxies "avoid" being located within ~3 Mpc of optical galaxies with red colors. Next, we consider the clustering properties of halo samples selected from the Bolshoi LambdaCDM simulation. A comparison with the clustering of ALFALFA galaxies suggests that galactic HI mass is not tightly related to host halo mass, and that a sizable fraction of subhalos do not host HI galaxies. Lastly, we find that we can recover fairly well the correlation function of HI galaxies by just excluding halos with low spin parameter. This finding lends support to the hypothesis that halo spin plays a key role in determining the gas content of galaxies.
    The Astrophysical Journal 08/2013; 776(1). · 6.73 Impact Factor
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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: The discovery of a previously unknown 21cm HI line source identified as an ultra-compact high velocity cloud in the ALFALFA survey is reported. The HI detection is barely resolved by the Arecibo 305m telescope ~4' beam and has a narrow HI linewidth (HPFW of 24 km/s). Further HI observations at Arecibo and with the VLA corroborate the ALFALFA HI detection, provide an estimate of the HI radius, ~1' at the 5 x 10^19 cm^-2 isophote, and show the cloud to exhibit rotation with an amplitude of ~9.0 +/- 1.5 km/s. In other papers, Rhode et al. (2013) show the HI source to have a resolved stellar counterpart and ongoing star forming activity, while Skillman et al. (2013) reveal it as having extremely low metallicity: 12 + log(O/H) = 7.16 +/- 0.04. The HI mass to stellar mass ratio of the object is found to be 2.6. We use the Tully-Fisher template relation in its baryonic form (McGaugh 2012) to obtain a distance estimate D = 1.3 (+0.9,-0.5) Mpc. Additional constraints on the distance are also provided by the optical data of Rhode et al. (2013) and McQuinn et al. (private communication), both indicating a distance in the range of 1.5 to 2.0 Mpc. The three estimates are compatible within their errors. The object appears to be located beyond the dynamical boundaries of, but still in close proximity to the Local Group. Its pristine properties are consistent with the sedate environment of its location. At a nominal distance of 1.75 Mpc, it would have an HI mass of ~1.0 x 10^6 Msun, a stellar mass of ~3.6 x 10^5 Msun, and a dynamical mass within the HI radius of ~1.5 x 10^7 Msun. This discovery supports the idea that optically faint - or altogether dark - low mass halos may be detectable through their non-stellar baryons.
    The Astronomical Journal 05/2013; 146(1). · 4.97 Impact Factor
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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 discovered recently in the Arecibo ALFALFA survey. In both observations, we are able to accurately measure the temperature sensitive [O III] 4363 Angstrom line and determine a "direct" oxygen abundance of 12 + log(O/H) = 7.17 +/- 0.04. Thus, Leo P is an extremely metal deficient (XMD) galaxy, and, indeed, one of the most metal deficient star-forming galaxies ever observed. For its estimated luminosity, Leo P is consistent with the relationship between luminosity and oxygen abundance seen in nearby dwarf galaxies. Leo P shows normal alpha element abundance ratios (Ne/O, S/O, and Ar/O) when compared to other XMD galaxies, but elevated N/O, consistent with the "delayed release" hypothesis for N/O abundances. We derive a helium mass fraction of 0.2509 +0.0184 -0.0123 which compares well with the WMAP + BBN prediction of 0.2483 +/- 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. It is possible that XMD galaxies may be divided into two classes: the relatively rare XMD emission line galaxies which are associated with starbursts triggered by infall of low-metallicity gas and the more common, relatively quiescent XMD galaxies like Leo P, with very low chemical abundances due to their intrinsically small masses.
    The Astronomical Journal 05/2013; 146(1). · 4.97 Impact Factor

Publication Stats

6k Citations
1,210.59 Total Impact Points

Institutions

  • 2014
    • Loyola University Maryland
      Baltimore, Maryland, United States
  • 1984–2014
    • 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
  • 2011
    • University of Colorado at Boulder
      • Department of Astrophysical and Planetary Sciences
      Boulder, Colorado, United States
  • 2008
    • Carnegie Mellon University
      • Department of Physics
      Pittsburgh, PA, United States
  • 2004
    • University of Cambridge
      • Institute of Astronomy
      Cambridge, England, United Kingdom
  • 1999
    • University of Minnesota Duluth
      Duluth, Minnesota, United States
  • 1998
    • New Mexico Institute of Mining and Technology
      • Department of Physics
      Socorro, New Mexico, United States
    • Wesleyan University
      • Department of Astronomy
      Middletown, Connecticut, United States
  • 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
  • 1983
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
  • 1978–1983
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States
    • Indiana University East
      Indiana, United States
  • 1976–1977
    • Indiana University Bloomington
      Bloomington, Indiana, United States