Panoramic GALEX far- and near-ultraviolet imaging of M31 and M33

David A. Thilker, Charles G. Hoopes, Luciana Bianchi, Samuel Boissier, R. Michael Rich, Mark Seibert, Peter G. Friedman, Soo Chang Rey, Veronique Buat, Tom A. Barlow, Yong Ik Byun, Jose Donas, Karl Forster, Timothy M. Heckman, Patrick N. Jelinsky, Young Wook Lee, Barry F. Madore, Roger F. Malina, D. Christopher Martin, Bruno MilliardPatrick F. Morrissey, Susan G. Neff, David Schiminovich, Oswald H.W. Siegmund, Todd Small, Alex S. Szalay, Barry Y. Welsh, Ted K. Wyder

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Abstract

We present Galaxy Evolution Explorer (GALEX) far-UV (FUV) and near-UV (NUV) mosaic observations covering the entirety of M31 and M33. For both targets, we measure the decline of surface brightness (in FUV and NUV) and changes in FUV - NUV color as a function of galactocentric radius. These UV radial profiles are compared to the distribution of ionized gas traced by Hα emission. We find that the extent of the UV emission, in both targets, is greater than the extent of the observed H II regions and diffuse ionized gas. We determine the ultraviolet diffuse fraction in M33 using our FUV observations and compare it to the Hα diffuse fraction obtained from wide-field narrowband imaging. The FUV diffuse fraction appears to be remarkably constant near 0.65 over a large range in galactocentric radius, with departures to higher values in circumnuclear regions and, most notably, at the limit of the Hα disk. We suggest that the increase in the FUV diffuse fraction at large galactocentric radii could indicate that a substantial portion of the diffuse emission beyond this point is not generated in situ but rather scattered from dust, after originating in the vicinity of the disk's outermost H II regions. The radial variation of the Ha diffuse fraction was also measured. We found the Ha diffuse fraction generally near 0.4 but rising toward the galaxy center, up to 0.6. We made no attempt to correct our diffuse fraction measurements for position-dependent extinction, so the quoted values are best interpreted as upper limits given the plausibly higher extinction for stellar clusters relative to their surroundings.

Original languageEnglish
Pages (from-to)L67-L70
JournalAstrophysical Journal
Volume619
Issue number1 II
DOIs
Publication statusPublished - 2005 Jan 20

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galaxies
extinction
gas
H II regions
ionized gases
radii
dust
narrowband
brightness
coverings
color
profiles
distribution
in situ
mosaic

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Thilker, D. A., Hoopes, C. G., Bianchi, L., Boissier, S., Rich, R. M., Seibert, M., ... Wyder, T. K. (2005). Panoramic GALEX far- and near-ultraviolet imaging of M31 and M33. Astrophysical Journal, 619(1 II), L67-L70. https://doi.org/10.1086/424816
Thilker, David A. ; Hoopes, Charles G. ; Bianchi, Luciana ; Boissier, Samuel ; Rich, R. Michael ; Seibert, Mark ; Friedman, Peter G. ; Rey, Soo Chang ; Buat, Veronique ; Barlow, Tom A. ; Byun, Yong Ik ; Donas, Jose ; Forster, Karl ; Heckman, Timothy M. ; Jelinsky, Patrick N. ; Lee, Young Wook ; Madore, Barry F. ; Malina, Roger F. ; Martin, D. Christopher ; Milliard, Bruno ; Morrissey, Patrick F. ; Neff, Susan G. ; Schiminovich, David ; Siegmund, Oswald H.W. ; Small, Todd ; Szalay, Alex S. ; Welsh, Barry Y. ; Wyder, Ted K. / Panoramic GALEX far- and near-ultraviolet imaging of M31 and M33. In: Astrophysical Journal. 2005 ; Vol. 619, No. 1 II. pp. L67-L70.
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abstract = "We present Galaxy Evolution Explorer (GALEX) far-UV (FUV) and near-UV (NUV) mosaic observations covering the entirety of M31 and M33. For both targets, we measure the decline of surface brightness (in FUV and NUV) and changes in FUV - NUV color as a function of galactocentric radius. These UV radial profiles are compared to the distribution of ionized gas traced by Hα emission. We find that the extent of the UV emission, in both targets, is greater than the extent of the observed H II regions and diffuse ionized gas. We determine the ultraviolet diffuse fraction in M33 using our FUV observations and compare it to the Hα diffuse fraction obtained from wide-field narrowband imaging. The FUV diffuse fraction appears to be remarkably constant near 0.65 over a large range in galactocentric radius, with departures to higher values in circumnuclear regions and, most notably, at the limit of the Hα disk. We suggest that the increase in the FUV diffuse fraction at large galactocentric radii could indicate that a substantial portion of the diffuse emission beyond this point is not generated in situ but rather scattered from dust, after originating in the vicinity of the disk's outermost H II regions. The radial variation of the Ha diffuse fraction was also measured. We found the Ha diffuse fraction generally near 0.4 but rising toward the galaxy center, up to 0.6. We made no attempt to correct our diffuse fraction measurements for position-dependent extinction, so the quoted values are best interpreted as upper limits given the plausibly higher extinction for stellar clusters relative to their surroundings.",
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Thilker, DA, Hoopes, CG, Bianchi, L, Boissier, S, Rich, RM, Seibert, M, Friedman, PG, Rey, SC, Buat, V, Barlow, TA, Byun, YI, Donas, J, Forster, K, Heckman, TM, Jelinsky, PN, Lee, YW, Madore, BF, Malina, RF, Martin, DC, Milliard, B, Morrissey, PF, Neff, SG, Schiminovich, D, Siegmund, OHW, Small, T, Szalay, AS, Welsh, BY & Wyder, TK 2005, 'Panoramic GALEX far- and near-ultraviolet imaging of M31 and M33', Astrophysical Journal, vol. 619, no. 1 II, pp. L67-L70. https://doi.org/10.1086/424816

Panoramic GALEX far- and near-ultraviolet imaging of M31 and M33. / Thilker, David A.; Hoopes, Charles G.; Bianchi, Luciana; Boissier, Samuel; Rich, R. Michael; Seibert, Mark; Friedman, Peter G.; Rey, Soo Chang; Buat, Veronique; Barlow, Tom A.; Byun, Yong Ik; Donas, Jose; Forster, Karl; Heckman, Timothy M.; Jelinsky, Patrick N.; Lee, Young Wook; Madore, Barry F.; Malina, Roger F.; Martin, D. Christopher; Milliard, Bruno; Morrissey, Patrick F.; Neff, Susan G.; Schiminovich, David; Siegmund, Oswald H.W.; Small, Todd; Szalay, Alex S.; Welsh, Barry Y.; Wyder, Ted K.

In: Astrophysical Journal, Vol. 619, No. 1 II, 20.01.2005, p. L67-L70.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Panoramic GALEX far- and near-ultraviolet imaging of M31 and M33

AU - Thilker, David A.

AU - Hoopes, Charles G.

AU - Bianchi, Luciana

AU - Boissier, Samuel

AU - Rich, R. Michael

AU - Seibert, Mark

AU - Friedman, Peter G.

AU - Rey, Soo Chang

AU - Buat, Veronique

AU - Barlow, Tom A.

AU - Byun, Yong Ik

AU - Donas, Jose

AU - Forster, Karl

AU - Heckman, Timothy M.

AU - Jelinsky, Patrick N.

AU - Lee, Young Wook

AU - Madore, Barry F.

AU - Malina, Roger F.

AU - Martin, D. Christopher

AU - Milliard, Bruno

AU - Morrissey, Patrick F.

AU - Neff, Susan G.

AU - Schiminovich, David

AU - Siegmund, Oswald H.W.

AU - Small, Todd

AU - Szalay, Alex S.

AU - Welsh, Barry Y.

AU - Wyder, Ted K.

PY - 2005/1/20

Y1 - 2005/1/20

N2 - We present Galaxy Evolution Explorer (GALEX) far-UV (FUV) and near-UV (NUV) mosaic observations covering the entirety of M31 and M33. For both targets, we measure the decline of surface brightness (in FUV and NUV) and changes in FUV - NUV color as a function of galactocentric radius. These UV radial profiles are compared to the distribution of ionized gas traced by Hα emission. We find that the extent of the UV emission, in both targets, is greater than the extent of the observed H II regions and diffuse ionized gas. We determine the ultraviolet diffuse fraction in M33 using our FUV observations and compare it to the Hα diffuse fraction obtained from wide-field narrowband imaging. The FUV diffuse fraction appears to be remarkably constant near 0.65 over a large range in galactocentric radius, with departures to higher values in circumnuclear regions and, most notably, at the limit of the Hα disk. We suggest that the increase in the FUV diffuse fraction at large galactocentric radii could indicate that a substantial portion of the diffuse emission beyond this point is not generated in situ but rather scattered from dust, after originating in the vicinity of the disk's outermost H II regions. The radial variation of the Ha diffuse fraction was also measured. We found the Ha diffuse fraction generally near 0.4 but rising toward the galaxy center, up to 0.6. We made no attempt to correct our diffuse fraction measurements for position-dependent extinction, so the quoted values are best interpreted as upper limits given the plausibly higher extinction for stellar clusters relative to their surroundings.

AB - We present Galaxy Evolution Explorer (GALEX) far-UV (FUV) and near-UV (NUV) mosaic observations covering the entirety of M31 and M33. For both targets, we measure the decline of surface brightness (in FUV and NUV) and changes in FUV - NUV color as a function of galactocentric radius. These UV radial profiles are compared to the distribution of ionized gas traced by Hα emission. We find that the extent of the UV emission, in both targets, is greater than the extent of the observed H II regions and diffuse ionized gas. We determine the ultraviolet diffuse fraction in M33 using our FUV observations and compare it to the Hα diffuse fraction obtained from wide-field narrowband imaging. The FUV diffuse fraction appears to be remarkably constant near 0.65 over a large range in galactocentric radius, with departures to higher values in circumnuclear regions and, most notably, at the limit of the Hα disk. We suggest that the increase in the FUV diffuse fraction at large galactocentric radii could indicate that a substantial portion of the diffuse emission beyond this point is not generated in situ but rather scattered from dust, after originating in the vicinity of the disk's outermost H II regions. The radial variation of the Ha diffuse fraction was also measured. We found the Ha diffuse fraction generally near 0.4 but rising toward the galaxy center, up to 0.6. We made no attempt to correct our diffuse fraction measurements for position-dependent extinction, so the quoted values are best interpreted as upper limits given the plausibly higher extinction for stellar clusters relative to their surroundings.

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Thilker DA, Hoopes CG, Bianchi L, Boissier S, Rich RM, Seibert M et al. Panoramic GALEX far- and near-ultraviolet imaging of M31 and M33. Astrophysical Journal. 2005 Jan 20;619(1 II):L67-L70. https://doi.org/10.1086/424816