Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aj....117.2757z&link_type=abstract
The Astronomical Journal, Volume 117, Issue 6, pp. 2757-2780.
Astronomy and Astrophysics
Astronomy
79
Galaxies: Individual: Ngc Number: Ngc 5907, Galaxies: Interactions, Galaxies: Photometry, Galaxies: Spiral
Scientific paper
Intrigued by the initial report of an extended luminosity distribution perpendicular to the disk of the edge-on Sc galaxy NGC 5907, we have obtained very deep exposures of this galaxy with a Schmidt telescope, large-format CCD, and intermediate-band filters centered at 6660 Å and 8020 Å. These two filters, part of a 15-filter set, are custom designed to avoid the brightest (and most variable) night skylines. As a result, our images are able to go deeper with lower sky noise than those taken with broadband filters at similar effective wavelengths: e.g., 0.6 e^- arcsec^-2 s^-1 for our observations versus 7.4 e^- arcsec^-2 s^-1 for the R-band measures of Morrison et al. In our assessment of both random and systematic errors, we show that the flux level where the errors of observation reach 1 mag arcsec^-2 are 29.00 mag arcsec^-2 in the 6660 Å image (corresponding to 28.7 in the R band) and 27.4 mag arcsec^-2 in the 8020 Å image (essentially on the I-band system). In a previous paper we have shown that NGC 5907 has a luminous ring around it, most plausibly caused by the tidal disruption of a dwarf spheroidal galaxy by the much more massive spiral. Here we show that, for values fainter than 27 R mag arcsec^-2, the surface brightness around NGC 5907 is strongly asymmetric, being mostly brighter on the northwest (ring) side of the galactic midplane. This asymmetry rules out a halo as the cause of the faint surface brightness we see. We find this asymmetry is likely an artifact resulting from a combination of ring light and residual surface brightness at faint levels from stars that our star-masking procedure cannot completely eliminate. The possible existence of an optical face-on warp in NGC 5907, suggested by our Very Large Array H I observations, is too confused with foreground star contamination to be independently studied. Good agreement with the surface photometry of NGC 5907 by other observers leads us to conclude that their data are similarly affected at faint levels by ring light and the residual effects of star masking procedures. Inspection of published images confirm this to be the case. Thus, we conclude that NGC 5907 does not have a faint extended halo.
Burstein David
Byun Yong-Ik.
Chen Jiansheng
Chen Rui
Chen Wen-Ping
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