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RISS 인기검색어
- 검색키워드
- 저자 : Michael A. Forster (검색결과 4 건)
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The <i>UV</i>–optical colour dependence of galaxy clustering in the local universe
Loh, Yeong-Shang,Rich, R. Michael,Heinis, Sé,bastien,Scranton, Ryan,Mallery, Ryan P.,Salim, Samir,Martin, D. Christopher,Wyder, Ted,Arnouts, Sté,phane,Barlow, Tom A.,Forster, Karl,Friedman Blackwell Publishing Ltd 2010 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.407 No.1
<P>ABSTRACT</P><P>We measure the UV-optical colour dependence of galaxy clustering in the local Universe. Using the clean separation of the red and blue sequences made possible by the <I>NUV</I>−<I>r</I> colour–magnitude diagram, we segregate the galaxies into red, blue and intermediate ‘green’ classes. We explore the clustering as a function of this segregation by removing the dependence on luminosity and by excluding edge-on galaxies as a means of a non-model dependent veto of highly extincted galaxies. We find that ξ(<I>r</I><SUB>p</SUB>, π) for both red and green galaxies shows strong redshift-space distortion on small scales – the ‘finger-of-God’ effect, with green galaxies having a lower amplitude than is seen for the red sequence, and the blue sequence showing almost no distortion. On large scales, ξ(<I>r</I><SUB>p</SUB>, π) for all three samples show the effect of large-scale streaming from coherent infall. On scales of 1 <I>h</I><SUP>−1</SUP> Mpc < <I>r</I><SUB>p</SUB> < 10 <I>h</I><SUP>−1</SUP> Mpc, the projected auto-correlation function <I>w</I><SUB>p</SUB>(<I>r</I><SUB>p</SUB>) for red and green galaxies fits a power law with slope γ∼ 1.93 and amplitude <I>r</I><SUB>0</SUB>∼ 7.5 and 5.3, compared with γ∼ 1.75 and <I>r</I><SUB>0</SUB>∼ 3.9 <I>h</I><SUP>−1</SUP> Mpc for blue sequence galaxies. Compared to the clustering of a fiducial <I>L</I>* galaxy, the red, green and blue have a relative bias of 1.5, 1.1 and 0.9, respectively. The <I>w</I><SUB>p</SUB>(<I>r</I><SUB>p</SUB>) for blue galaxies display an increase in convexity at ∼ 1 <I>h</I><SUP>−1</SUP> Mpc, with an excess of large-scale clustering. Our results suggest that the majority of blue galaxies are likely central galaxies in less massive haloes, while red and green galaxies have larger satellite fractions, and preferentially reside in virialized structures. If blue sequence galaxies migrate to the red sequence via processes like mergers or quenching that take them through the green valley, such a transformation may be accompanied by a change in environment in addition to any change in luminosity and colour.</P>
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Thilker, David A.,Bianchi, Luciana,Schiminovich, David,Gil de Paz, Armando,Seibert, Mark,Madore, Barry F.,Wyder, Ted,Rich, R. Michael,Yi, Sukyoung,Barlow, Tom,Conrow, Tim,Forster, Karl,Friedman, Peter IOP Publishing 2010 ASTROPHYSICAL JOURNAL LETTERS - Vol.714 No.1
<P>We have discovered recent star formation in the outermost portion ((1-4) x R(25)) of the nearby lenticular (S0) galaxy NGC 404 using Galaxy Evolution Explorer UV imaging. FUV-bright sources are strongly concentrated within the galaxy's Hi ring (formed by a merger event according to del Rio et al.), even though the average gas density is dynamically subcritical. Archival Hubble Space Telescope imaging reveals resolved upper main-sequence stars and conclusively demonstrates that the UV light originates from recent star formation activity. We present FUV, NUV radial surface brightness profiles, and integrated magnitudes for NGC 404. Within the ring, the average star formation rate (SFR) surface density (Sigma(SFR)) is similar to 2.2 x 10(-5) M(circle dot) yr(-1) kpc(-2). Of the total FUV flux, 70% comes from the H I ring which is forming stars at a rate of 2.5 x 10(-3) M(circle dot) yr(-1). The gas consumption timescale, assuming a constant SFR and no gas recycling, is several times the age of the universe. In the context of the UV-optical galaxy color-magnitude diagram, the presence of the star-forming Hi ring places NGC 404 in the green valley separating the red and blue sequences. The rejuvenated lenticular galaxy has experienced a merger-induced, disk-building excursion away from the red sequence toward bluer colors, where it may evolve quiescently or (if appropriately triggered) experience a burst capable of placing it on the blue/star-forming sequence for up to similar to 1 Gyr. The green valley galaxy population is heterogeneous, with most systems transitioning from blue to red but others evolving in the opposite sense due to acquisition of fresh gas through various channels.</P>
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The GALEX Ultraviolet Variability Catalog
Welsh, Barry Y.,Wheatley, Jonathan M.,Heafield, Kenneth,Seibert, Mark,Browne, Stanley E.,Salim, Samir,Rich, R. Michael,Barlow, Tom A.,Bianchi, Luciana,Byun, Yong-Ik,Donas, Jose,Forster, Karl,Friedman, American Institute of Physics 2005 The Astronomical journal Vol.130 No.2
<P>We present version 1.0 of the NASA Galaxy Evolution Explorer (GALEX) ultraviolet variability (GUVV) catalog, which contains information on 84 time-variable and transient sources gained with simultaneous near-ultraviolet (NUV) and far-ultraviolet (FUV) photometric observations. These time-variable sources were serendipitously revealed in the various 1<img entity='fdg' SRC='http://ej.iop.org/icons/Entities/fdg.gif' ALT='fdg' ALIGN='BASELINE' />2 diameter star fields currently being surveyed by the GALEX satellite in two ultraviolet bands (NUV 1750–2750 Å, FUV 1350–1750 Å) with limiting AB magnitudes of 23–25. The largest amplitude variable objects currently detected by GALEX are M dwarf flare stars, which can brighten by 5–10 mag in both the NUV and FUV bands during short-duration (<500 s) outbursts. Other types of large-amplitude ultraviolet variable objects include ab-type RR Lyrae stars, which can vary periodically by 2–5 mag in the GALEX FUV band. This first GUVV catalog lists galactic positions and possible source identifications in order to provide the astronomical community with a list of time-variable objects that can now be repeatedly observed at other wavelengths. We expect the total number of time-variable source detections to increase as the GALEX mission progresses, such that later version numbers of the GUVV catalog will contain substantially more variable sources.</P>
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