JPL: Black Holes Hide in Our Cosmic Backyard

[bystander]

Black Holes Hide in Our Cosmic Backyard
NASA | JPL-Caltech | NuSTAR | 2017 Jan 07

Click to view full size image 1 or image 2

IC 3639 -- Image Credit: NASA/JPL-Caltech/ESO/STScI
NGC 1448 -- Image Credit: NASA/JPL-Caltech/Carnegie-Irvine Galaxy Survey

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Monster black holes sometimes lurk behind gas and dust, hiding from the gaze of most telescopes. But they give themselves away when material they feed on emits high-energy X-rays that NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) mission can detect. That's how NuSTAR recently identified two gas-enshrouded supermassive black holes, located at the centers of nearby galaxies. ...

Both of these black holes are the central engines of what astronomers call "active galactic nuclei," a class of extremely bright objects that includes quasars and blazars. Depending on how these galactic nuclei are oriented and what sort of material surrounds them, they appear very different when examined with telescopes.

Active galactic nuclei are so bright because particles in the regions around the black hole get very hot and emit radiation across the full electromagnetic spectrum -- from low-energy radio waves to high-energy X-rays. However, most active nuclei are believed to be surrounded by a doughnut-shaped region of thick gas and dust that obscures the central regions from certain lines of sight. Both of the active galactic nuclei that NuSTAR recently studied appear to be oriented such that astronomers view them edge-on. That means that instead of seeing the bright central regions, our telescopes primarily see the reflected X-rays from the doughnut-shaped obscuring material. ...

Hunting hidden supermassive black holes
Durham University | 2017 Jan 07

IC 3639 - A New Bona Fide Compton-Thick AGN Unveiled by NuSTAR - Peter G. Boorman et al

• Astrophysical Journal 833(2):245 (20 Dec 2016) DOI: 10.3847/1538-4357/833/2/245
  arXiv.org > astro-ph > arXiv:1610.08997 > 27 Oct 2016

A New Compton-Thick AGN in Our Cosmic Backyard: Unveiling the Buried Nucleus in NGC 1448 with NuSTAR - A. Annuar et al

• arXiv.org > astro-ph > arXiv:1701.00497 > 02 Jan 2017

[Ann]

Very interesting!

Let's start with NGC 1448, also known as NGC 1457. According to Principal Galaxy Catalog, it is pretty much as luminous as the Milky Way, 20 billion stars like the sun versus 21 billion such stars for the Milky Way.

The colors of NGC 1448 are "normal", perhaps slightly on the red side for a galaxy that is classified as an Sc galaxy. Its U-B index is 0.010 and its B-V is 0.720. Normal, but a little bit red. Its far infrared magnitude is one magnitude brighter than its B magnitude. That's normal too, but in view of the fact that we see NGC 1448 nearly edge on, it means that the galaxy isn't all that dusty. Compare NGC 1448 with well-known edge-on galaxy NGC 891, which is two and a half magnitudes brighter in far infrared than in blue light! And since star formation produces blue starlight as well as infrared dust, we may conclude that there is not all that much star formation in NGC 1448. And not that much dust, either.

IC 3639, like NGC 1448, is pretty much exactly as luminous as the Milky Way, if we are to believe the Principal Galaxy Catalog. But IC 3639 is not only bluer than NGC 1448, but it is dustier, too. The B-V of IC 3639 is 0.550, not exceptionally blue for a face-on SBbc galaxy, but it is on the blue side, definitely. And its far infrared magnitude is almost two magnitudes brighter than its B magnitude, which is a lot for a face-on galaxy. So yes, there is quite a bit of star formation here and a lot of dust.

IC 3639 also appears to be "more purple" from X-rays than NGC 1448, so perhaps its black hole is more active.

Interesting!

Ann