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H {\Alpha} Imaging of Nearby Seyfert Host Galaxies

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H {\Alpha} Imaging of Nearby Seyfert Host Galaxies Draft version November 6, 2018 Preprint typeset using LATEX style emulateapj v. 5/2/11 Hα IMAGING OF NEARBY SEYFERT HOST GALAXIES Rachel L. Theios1 and Matthew A. Malkan and Nathaniel R. Ross2 Department of Physics and Astronomy, University of California, Los Angeles, 430 Portola Plaza, Los Angeles, CA 90095, USA Draft version November 6, 2018 ABSTRACT We used narrowband (∆λ = 70 Å) interference filters with the CCD imaging camera on the Nickel 1.0 meter telescope at Lick Observatory to observe 31 nearby (z < 0:03) Seyfert galaxies in the 12 µm Active Galaxy Sample (Spinoglio & Malkan 1989). We obtained pure emission line images of each galaxy, which reach down to a flux limit of 7:3 10−15 erg cm−2 s−1 arcsec−2, and corrected these images for [N ii] emission and extinction. We separated× the Hα emission line from the “nucleus” (central 100–1000 pc) from that of the host galaxy. The extended Hα emission is expected to be powered by newly formed hot stars, and indeed correlates well with other indicators of current SFRs in these galaxies: 7.7 µm PAH, far infrared, and radio luminosity. Relative to what is expected from recent star formation, there is a 0.8 dex excess of radio emission in our Seyfert galaxies. The Hα luminosity we measured in the galaxy centers is dominated by the AGN, and is linearly correlated with hard X-ray luminosity. There is, however, an upward offset of 1 dex in this correlation for Seyfert 1s, because their nuclear Hα emission includes a strong additional contribution from the Broad Line Region. We found a correlation between SFR and AGN luminosity. In spite of selection effects, we concluded that the absence of bright Seyfert nuclei in galaxies with low SFRs is real, albeit only weakly significant. We used our measured spatial distributions of Hα emission to determine what these Seyfert galaxies would look like when observed through fixed apertures (e.g. a spectroscopic fiber) at higher redshifts. Although all of these Seyfert galaxies would be detectable emission line galaxies at any redshift, most would appear dominated by (> 67%) their H ii region emission. Only −1 the most luminous AGN (log(LHα) > 41:5 erg s ) would still be identified as such at z 0:3. ∼ Subject headings: galaxies – active, galaxies – Seyfert, galaxies – star formation 1. INTRODUCTION et al. 2003) and at higher redshift (Juneau et al. 2011; Almost all observations of active galactic nuclei (AGN) Yan et al. 2011). suffer from the fact that the unresolved nonstellar emis- There are two strategies for dealing with the host sion is observed in combination with emission from the galaxy dilution problem. The first, taken by most studies surrounding host galaxy. The mixing of nonstellar con- of AGN beyond the local Universe, is to restrict consid- tinuum with the starlight of the galaxy (especially its eration only to “quasars,” i.e. extreme AGN in which the bright bulge) is a classic problem in the field (e.g. Malkan nonstellar nuclear emission strongly dominates over the & Filippenko 1983; Malkan & Oke 1983). A no less chal- host galaxy. This, however, ignores the largest popula- lenging problem is distinguishing the emission lines pow- tion of less luminous (or obscured) AGN, which may in ered by the central engine from those powered by hot fact be responsible for the majority of black-hole build- young stars in the host galaxy (Ho et al. 1997; Tom- ing in the Universe. The other approach, taken in this masin et al. 2008). In principle it is possible to separate paper, is to study these more typical AGN—the Seyfert the lines and continuum generated by stars from that of galaxies—by relying on spatially resolved observations. the central engine—they have several spectroscopic dif- The problem can in principle be solved with integral- ferences which are bigger than the range found among the field-unit spectroscopic maps of the full extents of nearby two components separately. However, spectroscopic sep- Seyfert galaxies. Here we use a simpler alternative, nar- rowband interference filter imaging of a representative arXiv:1604.00089v1 [astro-ph.GA] 1 Apr 2016 aration becomes increasingly difficult as the AGN contri- bution becomes weak relative to that of the host galaxy. sample of “common” Seyfert galaxies, to separate quan- This is exactly what happens as the active galaxy sys- titatively the emission lines powered by black hole accre- tem is observed through larger and larger apertures (i.e. tion in their centers from that by young stars throughout a slit or fiber spectrograph). Alternately, for a fixed ob- the host galaxies. serving aperture and other things being equal, the stellar Even with mediocre, uncorrected ground-based seeing, dilution fraction increases with increasing redshift of the our imaging is adequate to separate the central few hun- dred parsecs of Seyfert nuclei at z 0:01 from their active galaxy, out to z 2. This host dilution issue is ∼ relevant for studies that∼ have selected Seyfert galaxies host galaxies. This is sufficient for our purposes, since based on optical emission lines, both locally (Kauffmann nearly all of the AGN-powered line emission (from the Broad Line Region, BLR, and the Narrow Line Region, NLR) is confined to the central 100 parsecs, where it 1 Current address: Cahill Center for Astronomy and As- trophysics, California Institute of Technology, MS 249-17, usually dominates over line emission from H ii regions in Pasadena, CA 91125, USA the host galaxy. The results we obtain for these nearby 2 Current address: Raytheon Space and Airborne Systems, Seyfert galaxies can then be extended to predict how the 2000 E El Segundo Blvd, El Segundo, CA 90245, USA 2 Theios et al. Table 1 4th Quarter 12µm Seyfert Targets Target Name R. A. Decl. z Type Date On Filter Off Filter Exposure Seeing Weather (h:m:s) (d:m:s) (Å) (Å) (s) (arcsec) Mrk 79 07:42:32.8 +49:48:35 0.022189 Sy 1 2012 Dec 14 6710 6649 3600 2.3 Light cirrus 2013 Feb 10 6710 3600 2.9 Light cirrus NGC 2639 08:43:38.1 +50:12:20 0.011128 Sy 1 2012 Oct 19 6649 2700 1.8 Clear 2013 Feb 9 6520 2800 2.4 Clear NGC 3227 10:23:30.6 +19:51:54 0.003859 Sy 1 2012 Dec 14 6570 6520 2700 1.8 Light cirrus NGC 4051 12:03:30.6 +44:31:53 0.002336 Sy 1 2013 Feb 9 6570 6520 3100 2.4 Clear NGC 4151 12:10:32.6 +39:24:21 0.003319 Sy 1 2013 Feb 10 6570 6520 4000 2.9 Heavy cirrus NGC 5548 14:17:59.5 +25:08:12 0.017175 Sy 1 2013 Jul 3 6693 6606 2700 2.0 Clear NGC 7469 23:03:15.6 +08:52:26 0.016317 Sy 1 2012 Oct 7 6649 6520 2700 2.8 Clear NGC 7603 23:18:56.6 +00:14:38 0.029524 Sy 1 2012 Oct 8 6649 2700 1.7 Clear 2012 Oct 19 6737 2700 1.4 Clear NGC 4258 12:18:57.5 +47:18:14 0.001494 Sy 1.9 2013 Feb 9 6570 6520 2400 2.4 Light cirrus 2013 Feb 10 6570 6520 2400 2.9 Light cirrus NGC 4579 12:37:43.5 +11:49:05 0.005060 Sy 1.9 2013 Feb 9 6606 6520 3200 2.4 Cirrus NGC 5506 14:13:14.9 -03:12:27 0.006181 Sy 1.9 2013 Feb 9 6606 6520 3200 2.4 Cirrus NGC 262 00:48:47.1 +31:57:25 0.015034 Sy 2 2012 Oct 7 6649 6520 2700 2.2 Clear NGC 660 01:43:02.4 +13:38:42 0.002835 Sy 2 2013 Feb 10 6570 6520 1600 2.7 Light cirrus NGC 1068 02:42:40.7 -00:00:48 0.003793 Sy 2 2012 Oct 8 6570 6520 2700 1.9 Clear NGC 1056 02:42:48.3 +28:34:27 0.005154 Sy 2 2012 Oct 7 6606 6520 2700 2.1 Clear NGC 1144 02:55:12.2 -00:11:01 0.028847 Sy 2 2012 Oct 19 6737 6649 2700 2.0 Clear NGC 1194 03:03:49.1 -01:06:13 0.013596 Sy 2 2012 Oct 7 6649 6520 2700 2.3 Clear NGC 1241 03:11:14.6 -08:55:20 0.013515 Sy 2 2012 Oct 19 6649 6520 2700 1.7 Clear NGC 1320 03:24:48.7 -03:02:32 0.008883 Sy 2 2012 Oct 19 6606 6520 2700 1.6 Clear NGC 1667 04:48:37.1 -06:19:12 0.015167 Sy 2 2012 Oct 19 6649 6520 2700 1.9 Clear NGC 3079 10:01:57.8 +55:40:47 0.003723 Sy 2 2012 Dec 14 6570 6520 2700 1.8 Light cirrus NGC 4501 12:31:59.1 +14:25:13 0.007609 Sy 2 2013 Feb 10 6606 6520 3200 2.9 Heavy cirrus NGC 4941 13:04:13.1 -05:33:06 0.003696 Sy 2 2013 Feb 10 6520 2400 2.9 Light cirrus 2014 May 6 6570 4500 2.8 Clear NGC 5929 15:26:06.1 +41:40:14 0.008312 Sy 2 2014 May 20 6606 6520 2800 2.6 Light cirrus NGC 5953 15:34:32.4 +15:11:38 0.006555 Sy 2 2014 May 6 6520 4500 2.8 Clear 2014 May 20 6606 2600 2.6 Light cirrus NGC 6574 18:11:51.2 +14:58:54 0.007612 Sy 2 2013 Jul 17 6606 6520 2700 1.6 Clear NGC 7674 23:27:56.7 +08:46:45 0.028914 Sy 2 2012 Oct 19 6737 6606 2700 1.5 Clear Arp 220 15:34:57.1 +23:30:11 0.018126 LINER 2013 Jul 3 6693 6606 2700 2.0 Clear NGC 6384 17:31:24.3 +07:03:37 0.005554 LINER 2013 Jul 16 6606 6520 2700 1.8 Clear NGC 6670 18:33:35.4 +59:53:20 0.028853 non-Sy 2014 May 21 6737 6606 2100 1.9 Clear NGC 6764 19:08:16.4 +50:56:00 0.008059 LINER 2013 Jul 16 6606 6520 2700 1.4 Clear Note.
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