Hunting for Infrared Signatures of Supermassive Black Hole Activity in Dwarf Galaxies

Transcription

1 Hunting for Infrared Signatures of Supermassive Black Hole Activity in Dwarf Galaxies Kevin Hainline University of Arizona, Steward Observatory Amy Reines, NOAO Jenny Greene, Princeton University Daniel Stern, JPL / Caltech

2 McConnell and Ma (2013) M87 M31 NGC 3489 Milky Way GC The primordial seeds of supermassive black holes, and the origin of the M- σ relation, is not well understood. In recent years, dwarf galaxies have been targeted for exploring supermassive black hole growth.

3 McConnell and Ma (2013) M87 M31 NGC 3489 Milky Way GC? The primordial seeds of supermassive black holes, and the origin of the M- σ relation, is not well understood. In recent years, dwarf galaxies have been targeted for exploring supermassive black hole growth.

4 Greene (2012) Bromm & Yoshida (2011) Haehnelt & Rees (1993); Lodato & Natarajan (2006); Begelman et al. (2006); van Wassenhove et al. (2010) (see also Volonteri, Lodato & Natarajan 2008;Volonteri & Natarajan 2009) In addition, they may arise as the end product of very massive stars formed through stellar mergers in dense star clusters (Gürkan et al. 2004; Freitag et al. 2006; Goswami et al. 2012; Giersz et al. 2015; Lützgendorf et al. 2016)

5 We can use AGN emission to hunt for SMBHs in dwarf galaxies! Individual dwarf galaxies have been observed to host AGNs (Fillipenko & Ho 2003, Barth et al. 2004, Reines et al. 2011, among others) as well as systematic searches: X-ray Lemons et al. (2015) Optical Reines et al. (2013) see also: Mezcua et al. (2015), Pardo et al. (2016) see also: Greene & Ho (2004, 2007); Dong et al. (2012); Moran et al. (2014) At such low black hole masses, hunting for low luminosity AGNs in dwarf galaxies is difficult, especially when the host galaxies are strongly star-forming.

6 [W1] - [W2] Wright et al. (2010) The use of WISE colors to select AGNs in moderate and high mass galaxies has been demonstrated to be quite reliable (Jarrett et al. 2011, Stern et al. 2012, Mateos et al. 2012) However, how can WISE selection be used to select for AGNs in dwarf galaxies? [W2] - [W3]

7 [W1] - [W2] Wright et al. (2010) The use of WISE colors to select AGNs in moderate and high mass galaxies has been demonstrated to be quite reliable (Jarrett et al. 2011, Stern et al. 2012, Mateos et al. 2012) Jarrett et al. (2011) However, how can WISE selection be used to select for AGNs in dwarf galaxies? [W2] - [W3]

8 [W1] - [W2] Wright et al. (2010) The use of WISE colors to select AGNs in moderate and high mass galaxies has been demonstrated to be quite reliable (Jarrett et al. 2011, Stern et al. 2012, Mateos et al. 2012) Jarrett et al. (2011) However, how can WISE selection be used to select for AGNs in dwarf galaxies? Stern et al. (2012) [W2] - [W3]

9 Satyapal et al. (2014) and Sartori et al. (2015) used WISE photometry to explore the AGN content in bulgeless galaxies and dwarf galaxies. Satyapal et al. (2014) These results are different than what has been seen in dwarf galaxy AGN selection at other wavelengths. In addition, the BH occupation fraction is expected to drop steeply at these low masses. What is the origin of this relationship?

10 Wright et al. (2010) We know that the dust properties of dwarf galaxies are different than what is seen at higher masses! SBS E HST NICMOS Jarrett et al. (2011) 0.5 low-metallicity blue compact dwarf galaxy Stern et al. (2012) WISE Griffith et al. (2011) see: Hirashita & Hunt (2004), Reines et al. (2008), Izotov et al. (2011, 2014); Rémy-Ruyer et al. (2015) 1

11 Wright et al. (2010) We know that the dust properties of dwarf galaxies are different than what is seen at higher masses! SBS E HST NICMOS Jarrett et al. (2011) 0.5 low-metallicity blue compact dwarf galaxy Stern et al. (2012) WISE Griffith et al. (2011) see: Hirashita & Hunt (2004), Reines et al. (2008), Izotov et al. (2011, 2014); Rémy-Ruyer et al. (2015) 1

12 So. We examined the IR and optical properties of NASA Sloan Atlas (NSA) dwarf galaxies (M * < Msun, z < 0.055) using data from the AllWISE data release. What types of dwarf galaxies are mid-ir AGN selection techniques actually recovering?

13 Hainline et al. (submitted) Reines et al. (2013) We can start by looking at where optically-selected dwarf galaxy AGNs live in WISE color space, following Sartori et al. (2015).

14 Those objects that do sit in the Jarrett et al. (2011) WISE selection box have strong W1, W2, W3, and W4 photometry, indicative of an underlying IR power law from hot dust emission.

15 (templates from Assef et al. 2010) Those objects that do sit in the Jarrett et al. (2011) WISE selection box have strong W1, W2, W3, and W4 photometry, indicative of an underlying IR power law from hot dust emission.

16 We then looked at dwarf galaxies in the star-forming region of the BPT diagram. Objects with redder WISE colors are found in the lowmetallicity, high ionization region of the star-forming sequence. (Out of 18,482 dwarf galaxies with significant WISE detections, there are 14,013 with significant SDSS BPT emission line detections)

17 Optical g-r color SFR Surface Density Those objects with the reddest WISE colors are optically more blue than the bulk of the population, and have higher star formation rate densities.

18 Those objects with the reddest WISE colors have young stellar ages and high rates of ionizing photons, as estimated from Hα EW and luminosity.

19 We c a n u n d e r s t a n d t h e positions of galaxies in WISE color-color space as arising due to both the temperature a n d l u m i n o s i t y o f d u s t, compared to the host galaxy.

20 increasing dust temperature We c a n u n d e r s t a n d t h e positions of galaxies in WISE color-color space as arising due to both the temperature a n d l u m i n o s i t y o f d u s t, compared to the host galaxy.

21 increasing dust normalization We can understand the positions of galaxies in WISE color-color space as arising due to both the dust temperature and the relative luminosity of the dust emission, compared to the host galaxy.

22 We only find a sample of only 41 NSA objects (0.2%!) in our mass and redshift range with significant WISE photometry in the Jarrett et al. (2011) box. Their full SED properties vary for these objects. Multi-wavelength follow-up and full SED analysis is vital for selecting galaxies as AGNs!

23 We only find a sample of only 41 NSA objects (0.2%!) in our mass and redshift range with significant WISE photometry in the Jarrett et al. (2011) box. Their full SED properties vary for these objects. Multi-wavelength follow-up and full SED analysis is vital for selecting galaxies as AGNs!

24 We only find a sample of only 41 NSA objects (0.2%!) in our mass and redshift range with significant WISE photometry in the Jarrett et al. (2011) box. Their full SED properties vary for these objects. Multi-wavelength follow-up and full SED analysis is vital for selecting galaxies as AGNs!

25 We only find a sample of only 41 NSA objects (0.2%!) in our mass and redshift range with significant WISE photometry in the Jarrett et al. (2011) box. Their full SED properties vary for these objects. Multi-wavelength follow-up and full SED analysis is vital for selecting galaxies as AGNs!!

26 Conclusions The majority of optically-selected AGNs in dwarf galaxies have IR colors that are dominated by their host galaxies. Dwarf galaxies with the reddest WISE colors are compact, blue galaxies with young stellar ages and high star formation rate surface densities. Dwarf galaxies with extreme star-formation are capable of heating dust to temperatures producing W1 W2 > 0.8, (e.g. Stern et al. 2012), and this single color cut alone should not be used to select AGNs in dwarf galaxies. We provide a sample of 41 dwarf galaxies in the NSA which have WISE colors in the Jarrett et al. (2011) AGN selection box. We caution that follow-up observations are necessary to explore the presence of active massive black holes in the remaining 35 objects.