Back in the fall there was a special call for proposals for gap-filler snapshot observations for the Hubble Space Telescope. I submitted a proposal, along with Luis Ho and Minjin Kim, to get images of nearby active galaxies from the Swift-BAT AGN sample. Our proposal was approved, and the observations just started in late March. These observations are used to fill in small gaps in the HST observing schedule, and two other gap-filler proposals by other groups were also approved for imaging of different samples of galaxies. Our observations are short F814W (I-band) images from the ACS Wide-Field Camera. Our sample consists of AGNs from the Swift-BAT sample at redshifts below 0.1 that don’t already have HST imaging in I-band filters from previous programs, and there are 542 objects in our sample. Here’s one of our first images, Swift J0100.9-4750 (aka ESO 195-IG021). This cutout just shows a small part of the total ACS/WFC field of view.
Got up at 3:30 am for this one, but it was worth it.
Pictures taken from Parker Vista Point at UC Irvine.
Graduate student Benjamin Boizelle’s paper on ALMA observations of early-type galaxies was recently accepted for publication in the Astrophysical Journal. The paper presents observations of carbon monoxide line emission from dense molecular disks in the centers of 7 elliptical and lenticular galaxies, and describes the physical properties of these disks, which typically contain about 100 million Solar masses of molecular gas. One of our conclusions is that the disks are stable against gravitational fragmentation: because of a high rotational shear in the disks, it’s not easy for clumps to collapse and form stars in these systems. The next step will be to carry out dynamical modeling of the ALMA data to determine the masses of the central black holes in these galaxies, and Ben was recently awarded Hubble Space Telescope observing time to obtain near-infrared images of these galaxies in order to measure the distribution of stellar mass accurately, which is essential for the black hole mass measurement. Ben’s paper is posted at arxiv:1707.08229.
The European Space Agency chose one of our Hubble images for the “Picture of the Week” last month on spacetelescope.org. The image shows the central region of the nearby galaxy IC 342. This comes from Dan Carson’s Ph.D. thesis work on nuclear star clusters in spiral galaxies. The bright white spot in the center of the image is the nuclear star cluster, and IC 342’s cluster is one of the brightest and densest nuclear star clusters known. The radius of the central star cluster is about 4.6 light-years, as measured from the Hubble data, and it’s surrounded by many other smaller star clusters and young massive stars, as well as dark dust lanes containing dense gas. The galaxy is about 11 million light-years away, and is located in the constellation of Camelopardis.
(Trivia question: “Camelopardis!” was the catchphrase of what character on a 1970s sci-fi TV show?)
Congratulations to grad students Liuyi Pei and Dan Carson, who both completed their Ph.D. degrees this summer. Liuyi’s thesis work is on reverberation mapping of active galaxies, and she’s currently completing a paper on the big optical reverberation mapping campaign for NGC 5548 carried out by the AGN-STORM collaboration in 2014. She will be moving to the University of Illinois for a postdoctoral position, working with Yue Shen on the SDSS-RM project. Dan Carson’s thesis work involves studying the structural properties and stellar populations in nuclear star clusters in nearby spiral galaxies, using Hubble Space Telescope imaging data. He will be teaching physics this fall at Irvine Valley College and Chaffey College.
In September 2015, ALMA observed the center of the galaxy NGC 1332 at angular resolution 0.044 arcseconds as part of our group’s Cycle 3 program. We observed the CO(2-1) rotational emission line with the goal of mapping the rotation speed of the molecular disk at the center of the galaxy. We received the processed data from ALMA in January. The data clearly show the expected signature of a compact central mass, in the form of a central rise in rotation speed, and we fit dynamical models to the ALMA data cube to determine the central mass. This is the first ALMA observation that has resolved the radius of influence of a supermassive black hole, and the measurement gives the mass of the black hole in NGC 1332 to 10% precision. Here are links to our published paper in the Astrophysical Journal Letters and the preprint (for those who can’t directly access the journal paper).
Our group has been working on a project to measure the masses of supermassive black holes in nearby elliptical galaxies using observations from the Atacama Large Millimeter/submillimeter Array. Our strategy is to search the Hubble Space Telescope archives to find ellipticals that have very nice, round, flat dust disks around their nuclei, and then use ALMA to measure the rotation of these disks using the CO(2-1) emission line. We initially start with observations at about 0.3 arcsec resolution to check for the presence of high-velocity rotation within the black hole’s sphere of influence (the small region in the galaxy’s center where the black hole’s gravitational pull is the dominant force), and then, in cases where we see rapid rotation at small scales, we then propose for higher resolution observations to measure the black hole mass accurately. Our first paper from this project was recently accepted for publication in ApJ. It describes our overall strategy, the initial observations of NGC 1332, and our dynamical modeling method. We do see clear evidence of rapid rotation, but because these initial observations don’t fully resolve the black hole’s sphere of influence, we don’t yet get an accurate measurement of the black hole mass from this observation. Higher-resolution ALMA observations can do the job. A key takeaway point from the paper is that there are a lot of potential systematic errors that cause trouble if your observations don’t resolve the black hole’s sphere of influence, and we argue that in order to get precise and accurate measurements of black hole masses, resolving this sphere of influence region is really crucial.
You can find a prepreint here:
The AGN Key Project Team of Las Cumbres Observatory Global Telescope Network (LCOGT) just released our first team paper, describing the first reverberation mapping measurement ever done using 100% robotically-acquired data from ground-based telescopes. We used the LCOGT telescopes to obtain spectra and photometry of the active galaxy Arp 151 over a 200-day period from late 2014 through mid-2015, found strong variations in the nuclear luminosity, and used the data to measure the size of the broad-line emitting region and to derive constraints on the mass of the central black hole. There are only a few telesecopes in the world that are currently capable of doing fully robotic spectroscopic observations, and this is a great demonstration of the capabilities of the FLOYDS spectrographs on the LCOGT Faulkes Telescopes.
Our paper was accepted for publication in the Astrophysical Journal Letters, and a preprint is available at arXiv:1510.07329. Congratulations to Stefano Valenti, David Sand, Keith Horne, and the whole team!
Update: our paper is published now, and is highlighted on the AAS Nova web site.
Here’s the partially eclipsed moon starting to rise over the hills of eastern Orange County on September 27.
Last week I visited Oxford to attend a workshop on supermassive black holes at Wadham College. On friday we got to see the partial solar eclipse through thick clouds. I didn’t have the good camera with me, but here’s a picture from the phone camera that came out ok.