.233E The Astrophysical Journal, 321:233-250,19S7 October 1 © 1987. The American Astronomical Society. All rights reserved. Printed in U.S.A. .321. 1987ApJ. BROAD-BAND PROPERTIES OF THE CfA SEYFERT GALAXIES. II. INFRARED TO MILLIMETER PROPERTIES R. A. Edelson Owens Valley Radio Observatory, California Institute of Technology M. A. Malkan1,2 Department of Astronomy, University of California, Los Angeles AND G. H. Rieke Steward Observatory, University of Arizona Received 1986 November 14; accepted 1987 March 18 ABSTRACT Observations between 1.2 jum and 1.3 mm are presented for an unbiased, spectroscopically selected sample of 48 Seyfert galaxies. Most have complete infrared detections, but none were detected at 1.3 mm. The infrared spectra of optically selected Seyfert 2 galaxies are steep (a2.2_25/an= -1.56), in sharp contrast to optically selected quasars, which have flat infrared spectra (â2 2_25Aim = —1.09). This suggests that the infrared emission is predominantly thermal in Seyfert 2 galaxies and nonthermal in quasars. For optically selected Seyfert 1 galaxies, a2.2_25/im= -1.15, and -70% have flat spectra similar to quasars and unlike Seyfert 2 galaxies. Thus, the near- and mid-infrared emission from most Seyfert 1 galaxies appears to be dominated by non- thermal radiation, although thermal dust radiation is clearly important for others. Half of the objects detected at three or more IRAS wavelengths have far-infrared spectra which turn over shortward of 100 /un. For the relatively dust-free Seyfert 1 galaxies, this suggests that the infrared emission is dominated by unreprocessed radiation from a synchrotron self-absorbed source of the order of a light-day in size, about the same size as the hypothesized accretion disks. For the Seyfert 2 galaxies and other dusty objects, it implies minimum dust temperatures of 35-65 K, significantly warmer than dust in normal galaxies. In many of the objects with undetected turnovers, emission from cool dust in the galactic disk appears to mask the turnover. This strong “cool excess,” which dominates the 60-100 /mi emission from these objects, is correlated with the 11 /mi source size, suggesting that Seyfert nuclei tend to reside in galaxies undergoing strong star formation. Subject headings: galaxies: Seyfert — infrared: spectra — quasars — radiation mechanisms radio sources: galaxies — spectrophotometry I. INTRODUCTION thermally reradiate a significant portion of the optical and ultraviolet continuum (Rieke and Lebofsky 1979). The thermal Although Seyfert galaxies have been studied extensively at emission produces a very steep spectrum which curves down- near-infrared wavelengths (A < 10 /mi; cf. Rieke 1978, here- ward at shorter wavelengths, owing to the Wien cutoff* below after R78), the Infrared Astronomical Satellite (IRAS) all-sky the peak wavelength of emission from the hottest surviving survey at 12, 25, 60, and 100 /mi only recently provided the dust grains. Thermal far-infrared emission is also frequently first far-infrared detections of a significant number of active associated with dust reddening of the nuclear emission lines galactic nuclei (AGNs). Edelson and Malkan (1986, hereafter and nonstellar continuum. EM found correlations between EM) used IRAS, IUE, and ground-based data to study spec- steepness of the infrared spectra and internal reddening and tral energy distributions of a heterogeneous sample of other dust indicators. 29 AGNs between 0.1 and 100 /mi. Miley, Neugebauer, and However, some active galactic nuclei produce their infrared Soifer (1985) reported that far-infrared colors of 120 active continua by nonthermal processes. In the case of violently vari- galaxies. Neugebauer et al. (1986) reported IRAS observations able quasars and BL Lacertae objects, the rapid variability in of 179 quasars (of which 74 were detected in at least one IRAS the infrared and high polarization conclusively demonstrate wavelength), and Edelson (1986, hereafter E86) analyzed IRAS this (Angel and Stockman 1980). They also tend to have flat observations of the brightest PG/BQS quasars. Landau et al. infrared spectra (Impey and Neugebauer 1987). In quasars and (1986), Impey and Neugebauer (1987), and others have studied luminous, unreddened Seyfert 1 nuclei, the case for nonthermal the broad-band properties of blazars. infrared (and optical) emission is less direct, since the contin- Virtually every known Seyfert galaxy emits a large fraction uum is neither highly polarized nor violently variable. The of its total energy at infrared wavelengths. In some cases, this is strongest indication is the relatively flat shape of the far- the result of the presence of dust. The dust can absorb and infrared to optical continuum, which is well described by a a 1 power law with a> —1.3 (Fv oc v , EM). Optically selected Presidential Young Investigator. quasars have flat infrared spectra (â _ ^ = —1.09 E86), 2 Visiting Astronomer at the Infrared Telescope Facility, which is operated 2i2 25 by the University of Hawaii under contract to the National Aeronautics and which were identified as predominantly nonthermal emission. Space Administration. The correlation found between the 3.5 gm and 2 keV X-ray © American Astronomical Society • Provided by the NASA Astrophysics Data System .233E 234 EDELSON, MALKAN, AND RIEKE Vol. 321 .321. flux of quasars and Seyfert 1 galaxies (but not Seyfert 2 . turnover and the relation between far-infrared and millimeter galaxies) suggests that the same process is responsible for emis- emission are discussed in § IV. The relationship between infra- sion at both wavelengths, implying that the lower frequency red properties and those derived at other wavelengths are emission from these objects is nonthermal in origin (Malkan investigated in § V, and the 60 fim infrared luminosity function 1987ApJ. 1984). of Seyfert galaxies is derived and discussed in § VI. A summary In this paper, the infrared properties of a complete, of the major results of this paper is given in § VII. Positions of unbiased, spectroscopically selected sample of Seyfert galaxies six Seyfert galaxies which were not included in Paper I are are studied to determine the importance of different emission given in the Appendix. mechanisms. Previous AGN studies have been biased by the 1 -1 Throughout this paper, a value of H0 = 75 km s" Mpc selection techniques used to construct their samples. For is assumed. As the largest redshift in this sample is z = 0.06, no example, selection by ultraviolet excess (such as that used by corrections were made for cosmological effects in the lumi- Markarian 1972 and Schmidt and Green 1983) has been shown nosity distance or for evolution. to bias samples against strong infrared emitters (R78). This problem was avoided by examining the infrared to millimeter II. DATA spectral energy distributions of the CfA Seyfert galaxies—a a) Near-Infrared Data well-defined, unbiased, spectroscopically selected sample—to Near-infrared photometry was obtained with standard deduce the properties of the class as a whole. The CfA sample single-element InSb detectors on the Steward Observatory contains 26 type 1 and 22 type 2 Seyfert galaxies selected by Catalina 61 inch (1.55 m) reflector and the IRTF 3 m telescope. optical spectroscopy (Huchra and Berg 1987). Because of their The usual photometric bands, J (1.2 /un), JT (1.6 /mi), and K optical brightness, these objects are relatively easy to detect (2.2 /mi) were used, with absolute flux calibrations from and study at other wavelengths as well. Unlike objects selected Campins, Rieke, and Lebofsky (1985). New infrared photom- by ultraviolet excess, this sample has no known biases or selec- etry was obtained for 29 of the Seyfert galaxies in the near- tion effects due to dust content. The selection of the sample is infrared (1.1—2.2 /mi). Measurements of 13 bright objects were discussed in detail in Edelson (1987, hereafter Paper I), which also made at L (3.5 /mi) or L (3.6 /mi), and 12 objects were also described their radio properties. (One object, NGC 3227, observed at N (10.6 /mi). These observations were combined was incorrectly classified as a Seyfert 2 galaxy in Paper I). with those available in the literature (R78; Rudy, LeVan, and The near-infrared, IRAS, and millimeter-wave data are dis- Rodriguez Espinosa 1982; Cruz-Gonzales and Huchra 1984; cussed in the next section. The nature of the infrared contin- Devereux, Becklin, and Scoville 1987; Neugebauer et al 1987), uum emission is discussed in § III, and the far-infrared to provide near-infrared data for a total of 44 objects (95%), TABLE 1 CfA Seyfert Galaxy Near-Infrared Data Sl.2fim ^2.2nm $3.5 (im SlQ.6(xm Source (mJy) (mJy) (mJy) (mJy) (mJy) Date Mkn 334 14.3 ± 0.7 20.8 ± 1.0 27.5 ± 1.4 15 Mar 84 0048+29 11.1 ± 1.1 14.5 ± 1.4 15.6 ± 1.5 13 Sep 84 Mkn 993 13.8 ± 0.6 19.0 ± 0.7 16.0 ± 0.8 10 ± 18+4 21 Dec 86 Mkn 573 22.0 ± 2.0 29.5 ± 3.0 26.3 ± 2.4 23 ± 167 ± 15 26 Sep 85 0152+06 6.0 ± 0.4 8.0 ± 0.5 7.4 ± 0.5 16 Sep 84 NGC 1144 12.2 ± 2.4 29.4 ± 3.0 31.5 ± 3.6 158 ± 34 04 Mar 85 Mkn 1243 5.8 ± 0.6 7.4 ± 0.7 7.9 ± 0.8 Mar 86 NGC 3079 31.0 ± 2.2 71.3 ± 4.0 91.9 ± 5.0 73+6 210 ± 20 14 Apr 84 NGC 3362 5.8 ± 0.5 6.8 ± 0.6 5.2 ± 0.5 Mar 86 1058+45 Mkn 744 19.8 ± 2.0 25.9 ± 2.0 27.8 2.4 31+3 15 Apr 84 NGC 3982 9.2 ± 0.9 12.4 1.2 < 32 14 Apr 84 NGC 4235 21.1 ± 2.0 35.4 ± 3.0 29.9 2.4 22 + 2 16 Apr 84 Mkn 766 23.1 ± 2.0 42.6 ± 3.0 50.1 4.0 288 ± 28 Mar 86 NGC 4388 30.8 ± 2.0 48.5 ± 2.5 46.9 2.5 74 ± 04 Mar 85 NGC 5033 44.1 ± 3.5 61.6 ± 5.0 47.8 3.0 43 ± 3 < 144 04 Mar 85 Mkn 789