Category Archives: News

Mapping the rotation of a molecular gas disk around the supermassive black hole in NGC 3258

A new paper led by Benjamin Boizelle presents high-resolution ALMA observations of CO emission from the circumnuclear disk in NGC 3258. This is by far the best target we’ve found yet in our search for rotating molecular gas disks around black holes in elliptical galaxies, because we’re able to map the disk’s rotaiton deep within the black hole’s dynamical “sphere of influence” where the disk’s rotation gives a very direct measurement of the black hole mass. At 2.25 billion Solar masses, this is the largest black hole discovered yet with ALMA. You can read more about it in a press release from the National Radio Astronomy Observatory, or on the ALMA news site. Phil Plait also wrote about our NGC 3258 results on his “Bad Astronomy” blog.

Dr. Benjamin Boizelle

Benjamin Boizelle completed his Ph.D. in June 2018. His thesis research focused on measurement of black hole masses in elliptical galaxies using molecular gas kinematics, using observations from the Keck Observatory, the Hubble Space Telescope, and the ALMA Observatory. Ben will be starting a postdoctoral position in the fall at Texas A&M, where he will be continuing to work on supermassive black holes. Congratulations Ben!

Congratulations Thomas!

Undergraduate student Thomas Schmidt graduated from UCI with honors. His senior thesis project involved measurement of AGN light curves from several ground-based telescopes for programs coordinated with X-ray and UV monitoring being carried out with the Swift Observatory. Thomas earned multiple awards including Outstanding Senior in the Department of Physics and Astronomy.

First images from our new Hubble Space Telescope snapshot program

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.

New paper on ALMA observations of early-type galaxies

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.

ESA Picture of the Week

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 Liuyi Pei, Ph.D., and Dan Carson, Ph.D. !

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.

Measurement of the black hole mass in NGC 1332 from high-resolution ALMA observations

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).

Collaborators on this project include Benjamin Boizelle (UCI graduate student), Jeremy Darling (Colorado), Andrew Baker (Rutgers), David Buote (UCI), Luis Ho (KIAA), and Jonelle Walsh (Texas A&M).