POX 52: A Dwarf Seyfert 1 Galaxy with an Intermediate‐Mass Black Hole

Abstract

We describe new optical images and spectra of POX 52, a dwarf galaxy with an active nucleus that was originally detected in the POX objective-prism survey. While POX 52 was originally thought to be a Seyfert 2 galaxy, the new data reveal an emission-line spectrum very similar to that of the dwarf Seyfert 1 galaxy NGC 4395, with broad components to the permitted line profiles, and we classify POX 52 as a Seyfert 1 galaxy.The host galaxy appears to be a dwarf elliptical, and its brightness profile is best fit by a Sérsic model with an index of 3.6 ± 0.2 and a total magnitude of M V = −17.6. Applying mass-luminosity-linewidth scaling relations to estimate the black hole mass from the broad Hβ linewidth and nonstellar continuum luminosity, we find M BH ≈ 1.6 × 10 5 M ⊙ . The stellar velocity dispersion in the host galaxy, measured from the Ca II λ8498, 8542 Å lines, is 36 ± 5 km s −1 , also suggestive of a black hole mass of order 10 5 M ⊙ . Further searches for active nuclei in dwarf galaxies can provide unique constraints on the demographics of black holes in the mass range below 10 6 M ⊙ .

Black hole masses in active galaxies

“…The host galaxy was thought to be a dwarf spiral. More recent observations presented by Barth et al (2004) show that POX 52 is clearly a Seyfert 1 galaxy, and new imaging data shows the host galaxy to available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921304001334 be most likely a dwarf elliptical.…”

The mass function of nearby black hole candidates

“…We note that the total mass in stellar size black holes inside our Galaxy is estimated to be of the order of a few 10 9 M to which our law clearly does not connect. It is then reassuring that there is little evidence for black holes between 20 and 10 5 M (Barth et al 2004(Barth et al , 2005(Barth et al , 2008a(Barth et al ,b, 2009Greene et al 2006;Greene & Ho 2007a,b;Greene et al 2008), and there appears to be many black holes between 10 6 M and 10 7 M , but probably not enough to fill the distribution. These stellar black holes increase a factor to the cosmological density of black holes overall.…”

Formation of supermassive black holes

“…It is believed to contain a MBH of mass M BH ∼ 10 5 M (Barth et al, 2004). There are also significant non-detections of MBHs in a few nearby galaxies from stellardynamical observations, most notably the Local Group Scd-type spiral galaxy M33, in which the upper limit to M BH is just a few thousand solar masses (Gebhardt et al, 2001;Merritt et al, 2001).…”

“…These correlations may well extend down to the smallest masses. For example, the dwarf Seyfert 1 galaxy POX 52 is thought to contain a MBH of mass M BH ∼ 10 5 M (Barth et al, 2004).…”