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تسجيل مستخدم جديدSearching for Extragalactic Sources in the VISTA Variables in the Via Lactea Survey
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Laura D. Baravalle
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We search for extragalactic sources in the VISTA Variables in the Via Lactea survey that are hidden by the Galaxy. Herein, we describe our photometric procedure to find and characterize extragalactic objects using a combination of SExtractor and PSFEx. It was applied in two tiles of the survey: d010 and d115, without previous extragalactic IR detections, in order to obtain photometric parameters of the detected sources. The adopted criteria to define extragalactic candidates include CLASS_STAR < 0.3; 1.0 < R1/2 < 5.0 arcsec; 2.1 < C < 5; and Phi > 0.002 and the colors: 0.5 < (J - K_s) < 2.0 mag; 0.0 < (J - H) < 1.0 mag; 0.0 < (H - K_s) < 2.0 mag and (J - H) + 0.9 (H - K_s) > 0.44 mag. We detected 345 and 185 extragalactic candidates in the d010 and d115 tiles, respectively. All of them were visually inspected and confirmed to be galaxies. In general, they are small and more circular objects, due to the near-IR sensitivity to select more compact objects with higher surface brightness. The procedure will be used to identify extragalactic objects in other tiles of the VVV disk, which will allow us to study the distribution of galaxies and filaments hidden by the Milky Way.
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We report the first confirmed detection of the galaxy cluster VVV-J144321-611754 at very low latitudes (l = 315.836$^{circ}$, b = -1.650$^{circ}$) located in the tile d015 of the VISTA Variables in the Via Lactea (VVV) survey. We defined the region o
f 30$times$ 30 $arcmin^2$ centered in the brightest galaxy finding 25 galaxies. For these objects, extinction-corrected median colors of (H - K$_{s}$) = 0.34 $pm$ 0.05 mag, (J - H) = 0.57 $pm$ 0.08 mag and (J - K$_{s}$) = 0.87 $pm$ 0.06 mag, and R$_{1/2}$ = 1.59 $pm$ 0.16 $arcsec$; C = 3.01 $pm$ 0.08; and Sersic index, n = 4.63 $pm$ 0.39 were estimated. They were visually confirmed showing characteristics of early-type galaxies in the near-IR images. An automatic clustering analysis performed in the whole tile found that the concentration of galaxies VVV-J144321-611754 is a real, compact concentration of early-type galaxies. Assuming a typical galaxy cluster with low X-ray luminosity, the photometric redshift of the brightest galaxy is $z = $ 0.196 $pm$ 0.025. Follow-up near-IR spectroscopy with FLAMINGOS-2 at the Gemini-South telescope revealed that the two brighter cluster galaxies have typical spectra of early-type galaxies and the estimated redshift for the brightest galaxy VVV-J144321.06-611753.9 is $z =$ 0.234$pm$0.022 and for VVV-J144319.02-611746.1 is $z =$ 0.232$pm$0.019. Finally, these galaxies clearly follow the cluster Red Sequence in the rest-frame near-IR color--magnitude diagram with the slope similar to galaxy cluster at redshift of 0.2. These results are consistent with the presence of a bona fide galaxy cluster beyond the Milky Way disk.
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