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Pre-print draft: arXiv:1504.01744
Journal: The The Astrophysical Journal Supplement Series, Volume 219, Issue 2

Spitzer Point-Source Catalogs of ∼300,000 Stars in Seven Nearby Galaxies
Rubab Khan, K. Z. Stanek, C. S. Kochanek, George Sonneborn


We present Spitzer IRAC 3.6μm-8μm and MIPS 24μm point-source catalogs for seven galaxies: NGC 6822, M33, NGC 300, NGC 2403, M81, NGC 0247, and NGC 7793. The catalogs contain a total of ∼300,000 sources and were created by dual-band selection of sources with >3 sigma detections at both 3.6μm and 4.5μm. The source lists become incomplete near m_3.6=m_4.5≅18. We complement the 3.6μm and 4.5μm fluxes with 5.8μm, 8.0um and 24μm fluxes or 3 sigma upper limits using a combination of PSF and aperture photometry. This catalog is a resource as an archive for studying mid-infrared transients and for planning observations with the James Webb Space Telescope.


Figure 1

Fig. 1.— The IRAC 3.6 um images of the seven targeted galaxies: NGC 6822, M33, NGC 300, NGC 2403, M81, NGC 0247, and NGC 7793. The red line on each figure spans 10'.

Figure 2

Fig. 2.— The distances (in pixels) to the nearest 3.6μm source for each 4.5μm source in M 33 along the x-axis and y-axis of the images. The blue and red histograms show the distance distributions. The radius of the concentric circles are 0.5 pixel (green) and 1 pixel (black). In this case, most sources (>90%) have a match within 0.5 pixels, and the density of nearest matches falls rapidly between 0.5-1.0 pixel (<10% additional matches) while the number of duplicate matches increase (<0.5% duplicate matches). At larger distances, the distribution essentially flattens. Similiar distributions are observed for the other six galaxies (see Table 1).

Table 1

Table 1 — Catalog Statistics.

Figure 3

Fig. 3.— The differences between aperture and PSF photometry magnitudes as a function of the PSF magnitudes for the m_psf<15 sources in NGC 6822 and M81. For the less crowded case of NGC 6822, the two measurements generally agree in all four IRAC bands, with the scatter increasing for the fainter sources. The same is true for the 3.6μm and 4.5μm images of M81, but at 5.8μm, the scatter increases rapidly, and for 8.0um the situation worsens further.

Figure 4

Fig. 4.— The m_4.5 vs. m_3.6-m_4.5 (top-row), m_5.8 vs. m_4.5-m_5.8 (middle-row), and m_8.0 vs. m_5.8-m_8.0 (bottom-row) color magnitude diagrams (CMDs) for the >3 sigma sources in NGC 6822, M33, NGC 300 and NGC 2403. The red lines represent isodensity contours.

Figure 5

Fig. 5.— Same as Figure 4, but for the galaxies M81, NGC 247, NGC 7793, and (for comparison) a 6 square-degree region of the NOAO Bootes Field from the Spitzer Deep Wide Field Survey (SDWFS, Ashby et al. 2009) data.

Figure 6

Fig. 6.— Apparent magnitude histograms for all the sources in the catalog, with the shaded regions showing the sources in M33. Overall, the source lists become incomplete at (locations marked by the dashed lines) m_3.6≳18, m_4.5≳18, m_5.8≳17 and m_8.0≳16. The M 33 source-list is roughly ∼0.5 mag shallower than for the other galaxies. The dotted lines show the apparent-magnitude histograms of the SDWFS catalog sources (scaled-up by a factor of x15 for clarity).

Figure 7

Fig. 7.— Mid-IR color histograms for all the sources in the catalog, with the shaded histograms showing the distribution of sources with 1 sigma uncertainty in color ≲0.2. The sharp peak of color distribution at m_3.6-m_4.5≅0 is due to the Rayleigh-Jeans tail of the spectra of all normal stars. The longer wavelengths are increasingly dominated by dusty stars, with color distribution peaks at (locations marked by the dashed lines) m_3.6-m_5.8=m_4.5-m_5.8≅1, m_3.6-m_8.0=m_4.5-m_8.0≅2, and m_5.8-m_8.0≅1. The dotted lines show the mid-IR color histograms of the SDWFS catalog sources (scaled-up by a factor of x15 for clarity).


Table 2

Table 2 — Catalog for 30,745 Point Sources in NGC 6822. Full table.

Table 3

Table 3 — Catalog for 78,841 Point Sources in M33. Full table.

Table 4

Table 4 — Catalog for 21,739 Point Sources in NGC 300. Full table.

Table 5

Table 5 — Catalog for 17,022 Point Sources in NGC 2403. Full table.

Table 6

Table 6 — Catalog for 28,674 Point Sources in M81. Full table.

Table 7

Table 7 — Catalog for 16,658 Point Sources in NGC 247. Full table.

Table 8

Table 8 — Catalog for 5,617 Point Sources in NGC 7793. Full table.



This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration (NASA). We extend our gratitude to the SINGS Legacy Survey and the LVL Survey for making their data publicly available. RK is supported through a JWST Fellowship hosted by the Goddard Space Flight Center and awarded as part of the NASA Postdoctoral Program operated by the Oak Ridge Associated Universities on behalf of NASA.

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