Martin J. Meyer

Space Telescope Science Institute, Baltimore, Maryland, United States

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Publications (8)29 Total impact

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    ABSTRACT: We perform an analysis of the spatial clustering properties of HI selected galaxies from the HI Parkes All Sky Survey (HIPASS) using the formalism of the halo occupation distribution (HOD). The resulting parameter constraints show that the fraction of satellite galaxies (i.e. galaxies which are not the central member of their host dark matter halo) among HIPASS galaxies is <20%, and that satellite galaxies are therefore less common in HIPASS than in optically selected galaxy redshift surveys. Moreover the lack of fingers-of-god in the redshift space correlation function of HIPASS galaxies may indicate that the HI rich satellites which do exist are found in group mass rather than cluster mass dark matter halos. We find a minimum halo mass for HIPASS galaxies at the peak of the redshift distribution of M~10^11 solar masses, and show that less than 10% of baryons in HIPASS galaxies are in the form of HI. Quantitative constraints on HOD models from HIPASS galaxies are limited by uncertainties introduced through the small survey volume. However our results imply that future deeper surveys will allow the distribution of HI with environment to be studied in detail via clustering of HI galaxies. Comment: 11 pages, 5 figures. Submitted to MNRAS
    08/2009;
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    ABSTRACT: We present HST images in which we discovered the presence of a large number of massive stars in the field of the two galaxies NGC 1313 and NGC 4449. These massive stars, not in obvious groups or clusters, are known to produce a significant amount of UV radiation, and to live for at most 25 Myr. We think that these stars are the main source of diffuse UV emission first observed by Meurer et al. (1995) in starburst galaxies. We also propose that the infant mortality of star clusters, an early evolutionary stage of star clusters which kills 90% of them within 10 Myr, is a physical process that can explain how these young stars could end up in the field so quickly. We will also present preliminary stellar 2-points correlation functions for the two galaxies.
    02/2009: pages 1-6;
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    ABSTRACT: We present Spitzer imaging of the metal-deficient (Z 30% Z☉) Local Group dwarf galaxy NGC 6822. On spatial scales of ~130 pc, we study the nature of IR, Hα, H I, and radio continuum emission. Nebular emission strength correlates with IR surface brightness; however, roughly half of the IR emission is associated with diffuse regions not luminous at Hα (as found in previous studies). The global ratio of dust to H I gas in the ISM, while uncertain at the factor of ~2 level, is ~25 times lower than the global values derived for spiral galaxies using similar modeling techniques; localized ratios of dust to H I gas are about a factor of 5 higher than the global value in NGC 6822. There are strong variations (factors of ~10) in the relative ratios of Hα and IR flux throughout the central disk; the low dust content of NGC 6822 is likely responsible for the different Hα/IR ratios compared to those found in more metal-rich environments. The Hα and IR emission is associated with high column density (1021 cm-2) neutral gas. Increases in IR surface brightness appear to be affected by both increased radiation field strength and increased local gas density. Individual regions and the galaxy as a whole fall within the observed scatter of recent high-resolution studies of the radio-far-IR correlation in nearby spiral galaxies; this is likely the result of depleted radio and far-IR emission strengths in the ISM of this dwarf galaxy.
    The Astrophysical Journal 12/2008; 652(2):1170. · 6.73 Impact Factor
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    ABSTRACT: We present Spitzer observations of the nearby dwarf starburst galaxy NGC 1705 obtained as part of the Spitzer Infrared Nearby Galaxies Survey. The galaxy morphology is very different shortward and longward of ~5 μm: optical and short-wavelength IRAC imaging shows an underlying red stellar population, with the central super star cluster (SSC) dominating the luminosity; longer wavelength IRAC and MIPS imaging reveals warm dust emission arising from two off-nuclear regions that are offset by ~250 pc from the SSC and that dominate the far-IR flux of the system. These regions show little extinction at optical wavelengths. The galaxy has a relatively low global dust mass (~2 × 105 M☉, implying a global dust-to-gas mass ratio ~2-4 times lower than the Milky Way average, roughly consistent with the metallicity decrease). The off-nuclear dust emission appears to be powered by photons from the same stellar population responsible for the excitation of the observed Hα emission; these photons are unassociated with the SSC (although a contribution from embedded sources to the IR luminosity of the off-nuclear regions cannot be ruled out). Low-resolution IRS spectroscopy shows moderate-strength PAH emission in the 11.3 μm band in the more luminous eastern peak; no PAH emission is detected in the SSC or the western dust emission complex. There is significant diffuse emission in the IRAC 8 μm band after starlight has been removed by scaling shorter wavelength data; the fact that IRS spectroscopy shows spatially variable PAH emission strengths compared to the local continuum within this diffuse gas suggests caution in the interpretation of IRAC diffuse 8 μm emission as arising from PAH carriers alone. The nebular metallicity of NGC 1705 falls at the transition level of ~0.35 Z☉ found by Engelbracht and collaborators, below which PAH emission is difficult to detect; the fact that a system at this metallicity shows spatially variable PAH emission demonstrates the complexity of interpreting diffuse 8 μm emission in galaxies. NGC 1705 deviates significantly from the canonical far-infrared versus radio correlation, having significant far-infrared emission but no detected radio continuum.
    The Astrophysical Journal 12/2008; 647(1):293. · 6.73 Impact Factor
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    ABSTRACT: We present observations of the dust and atomic gas phase in seven dwarf irregular galaxies of the M81 group from the Spitzer SINGS and VLA THINGS surveys. The Spitzer observations provide a first glimpse of the nature of the nonatomic ISM in these metal-poor (Z ~ 0.1 Z☉), quiescent (SFR ~ 0.001-0.1 M☉ yr-1) dwarf galaxies. Most detected dust emission is restricted to H I column densities >1 × 1021 cm-2, and almost all regions of high H I column density (>2.5 × 1021 cm-2) have associated dust emission. Spitzer spectroscopy of two regions in the brightest galaxies (IC 2574 and Holmberg II) show distinctly different spectral shapes and aromatic features, although the galaxies have comparable gas-phase metallicities. This result emphasizes that the strength of the aromatic features is not a simple linear function of metallicity. We estimate dust masses of ~104-106 M☉ for the M81 dwarf galaxies, resulting in an average dust-to-gas ratio (Mdust/MH I) of ~3 × 10-4 (1.5 × 10-3 if only the H I that is associated with dust emission is considered); this is an order of magnitude lower than the typical value derived for the SINGS spirals. The dwarf galaxies are underluminous per unit star formation rate at 70 μm as compared to the more massive galaxies in SINGS by a factor of ~2. However, the average 70/160 μm ratio in the sample dwarf galaxies is higher than what is found in the other galaxies of the SINGS sample. This can be explained by a combination of a lower dust content in conjunction with a higher dust temperature in the dwarfs.
    The Astrophysical Journal 12/2008; 661(1):102. · 6.73 Impact Factor
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    ABSTRACT: We examine the clustering properties of H I-selected galaxies through an analysis of the H I Parkes All-Sky Survey Catalogue (HICAT) two-point correlation function. Various subsamples are extracted from this catalog to study the overall clustering of H I-rich galaxies and its dependence on luminosity, H I gas mass, and rotational velocity. These samples cover the entire southern sky δ < 0°, containing up to 4174 galaxies over the radial velocity range 300-12,700 km s-1. A scale length of r0 = 3.45 ± 0.25 h-1 Mpc and slope of γ = 1.47 ± 0.08 is obtained for the H I-rich galaxy real-space correlation function, making gas-rich galaxies among the most weakly clustered objects known. H I-selected galaxies also exhibit weaker clustering than optically selected galaxies of comparable luminosities. Good agreement is found between our results and those of synthetic H I-rich galaxy catalogs generated from the Millennium Run cold dark matter (CDM) simulation. Bisecting HICAT using different parameter cuts, clustering is found to depend most strongly on rotational velocity and luminosity, while the dependency on H I mass is marginal. Splitting the sample around vrot = 108 km s-1, a scale length of r0 = 2.86 ± 0.46 h-1 Mpc is found for galaxies with low rotational velocities compared to r0 = 3.96 ± 0.33 h-1 Mpc for the high rotational velocity sample.
    The Astrophysical Journal 12/2008; 654(2):702. · 6.73 Impact Factor
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    ABSTRACT: We present the first results of a new technique to detect, locate, and characterize young dissolving star clusters. Using HST/ACS archival images of the nearby galaxy IC2574, we performed stellar PSF photometry and selected the most massive stars as our first test sample. We used a group-finding algorithm on the selected massive stars to find cluster candidates. We then plot the color-magnitude diagrams for each group, and use stellar evolutionary models to estimate their age. So far, we found 79 groups with ages of up to about 100 Myr, displaying various sizes and densities. Comment: 7 pages including 11 figures. Talk given at the meeting on "Young massive star clusters - Initial conditions and environments", E. Perez, R. de Grijs, R. M. Gonzalez Delgado, eds., Granada (Spain), September 2007, Springer: Dordrecht
    Astrophysics and Space Science 02/2008; · 2.06 Impact Factor
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    ABSTRACT: The role that massive stars play in the dust content of the Universe is extremely uncertain. It has long beenhypothesized that dust can condense within the ejecta of supernovae (SNe), however there is a frustratingdiscrepancy between the amounts of dust found in the early Universe, or predicted by nucleation theory, andinferred from SN observations. Our SEEDS collaboration has been carefully revisiting the observational casefor dust formation by core-collapse SNe, in order to quantify their role as dust contributors in the earlyUniverse. As dust condenses in expanding SN ejecta, it will increase in optical depth, producing threesimultaneously observable phenomena: (1) increasing optical extinction; (2) infrared (IR) excesses; and (3)asymmetric blue-shifted emission lines. Our SEEDS collaboration recently reported all three phenomenaoccuring in SN2003gd, demonstrating the success of our observing strategy, and permitting us to derive a dustmass of up to 0.02 solar masses created in the SN. To advance our understanding of the origin and evolution ofthe interstellar dust in galaxies, we propose to use HST's WFPC2 and NICMOS instruments plus Spitzer'sphotometric instruments to monitor ten recent core-collapse SNe for dust formation and, as a bonus, detect lightechoes that can affect the dust mass estimates. These space-borne observations will be supplemented by ground-based spectroscopic monitoring of their optical emission line profiles. These observations would continue our 2-year HST and Spitzer monitoring of this phenomena in order to address two key questions: Do all SNe producedust? and How much dust do they produce? As all the SN are witin 15 Mpc, each SN stands an excellentchance of detection with HST and Spitzer and of resolving potential light echoes.
    Spitzer Proposal. 04/2007; -1:40010.