A team led by Dr. Jae-Woo Kim, and including myself, has just published a paper in the Astrophysical Journal Letters about the discovery of a very large structure called a supercluster at a redshift of z~1. Dr. Kim used near-infrared observations of the SSA22 field from the Infrared Medium-Deep survey (IMS) to identify massive galaxies beyond our local Universe. He then utilized optical spectroscopy with the IMACS multi-object spectrograph on the Magellan telescope (in Chile) to pinpoint the exact distance of these galaxies from us and therefore identify possible spatial associations between them, called galaxy clusters. Not only did he discover galaxy clusters, but their proximity to each other implies that they are actually part of the same super-structure, also called a galaxy supercluster.

The properties of such large scale (>10 Mpc) structures can be used to put the Lambda-Cold-Dark-Matter, the currently accepted theoretical framework of our Universe, to the test. As this is one of the most massive structures ever found at similar redshifts, it provides a robust test to our understanding of how matter and structures evolve in the Universe. While the detection of this supercluster does not contradict the expectations of the Lambda-CDM model, the confirmation of two additional supercluster candidates in the same field would create tension between observations and theoretical expectations.

The paper should appear shortly online. Yet another exciting result from the IMS (after this and this)!

The IMS team is hard at work to acquire more spectroscopic data and to analyze already existing photometric and spectroscopic data to probe further into the question of how galaxies have evolved into the structures we observe in the local Universe! 

Given my interest in performing Astronomy outreach and communicating science with the public, I have been a member of Working Group 2 of Commision C2 of the International Astronomical Union (IAU) "Communicating Astronomy with the Public (CAP)". I am also a member of the SOC for the next CAP conference that will take place in Colombia in May 2016. The conference plans to bring together astronomy communicators, outreach officials, and educators from all around the world to discuss how to best communicate astronomy with the public and the challenges that science communicators face in the era of social media!

The registration for the conference is now open. You can click below to go to the CAP2016 website!

For the last several months I have been working hard on Gemini Integral Field Unit spectroscopic data of 6 nearby Type 2 AGN, looking at their narrow line region kinematics in an effort to characterize their outflows. The first paper is now out on the arXiv and is currently in press to appear in the Astrophysical Journal!

We find ubiquitous evidence for outflowing gas in these 6 Type 2 AGN selected from our previous study on 39,000 Type 2 AGN in the local Universe, drawn from the SDSS survey. These objects were selected based on their extreme [OIII] emission line profile shapes in their spatially integrated SDSS spectra. Using the Gemini GMOS Integral Field Unit (IFU) spectrograph, we could get spatially resolved spectroscopic information of the central several kpc of these objects and study the kinematics of their ionized gas in detail. 

Surprisingly, we found clear evidence that the narrow line region kinematics appear to be a superposition of two distinct kinematic components. The first one is driven by the gravitational potential of the galaxy. How do we know this? We find clear rotation signatures for the "core" component of the Halpha-emitting gas. This rotation matches perfectly with the rotation of the stars in the same region. The second kinematic component shows up as gas at extreme velocities that is several times the velocity of the stars. Moreover, the measured velocity is significantly different from the systemic (average) velocity of the galaxy. This component is particularly strong for the [OIII] emission line but is also detected in the Halpha emission, albeit weaker.

We are able to decompose these two components and study their spatial distributions separately. While the gravitational component is spatially extended, reaching the edge of the field of view of our instrument, the non-gravitational component is much more compact, in some cases only marginally resolved with our seeing-limited observations (our data can resolved spatial scales of ~<1 kpc). Interestingly, and for the first time compared to previous studies, we can use the radial profile of the kinematics of these two components to accurately measure the size of the region within which the non-gravitational component dominates the kinematics of the ionized gas. This is the size of the outflow.

Intriguingly, we find that outflows in all 6 objects range between 1.3 to 2 kpc in size. This is only a small fraction of the size of these galaxies (with typical effective radii of >6 kpc). What is more, if we consider methods previously used in the literature that rely on photometric data (flux of [OIII] for example) to measure the outflow sizes, we overestimate the outflow size by a factor of 2 at least. If Halpha is used as a size determinator, the outflow size is even more severely overestimated. This finding has important reprecussions regarding both the assumed lifetimes of these outflows and the fraction of their host galaxy that they can affect.

We are currently finalizing a second paper on the same data set, where we look at the photoionization properties of these sources to understand what is driving these extreme kinematics. We also calculate the energetics of these outflows by utilizing our updated knowledge of their true, kinematic, size. 

Spoiler alert: These outflows, at least at the AGN luminosities that we are probing with our sample, do not seem to be able to affect their hosts.

The amazing people and my former colleagues and ongoing collaborators at CEOU made a cool video of a supernova bursting in the galaxy NGC 2442, roughly 80 million light years away from Earth. Observations where taken with the Lee Sang Gak 17-inch robotic telescope in Australia. You can clearly see the empty space before the explosion, the sudden brightening, and slow decrease of the supernova emission. From the analysis of lightcurves at several optical and near-infrared bands, they think that the explosion was possibly caused by the interaction between a white dwarf star and a main sequence star with a size of 0.1 - 1.0 times the size of our Sun.

Plus points for the creepy music background!

Follow the link to check out the video on YouTube!

I have a confession to make...I have a grammar pet peeve.

So yesterday I received the proofs of my recently accepted paper on the single-epoch black hole mass estimator comparisons. I have two days to go through the edited paper and see if everything reads and looks as it should. This is my last opportunity to make small changes to the layout and content of the paper before it goes to the publisher.

As it turns out, the person in charge of editing my paper decided to change all the instances of "AGN" in my paper to "AGNs". As soon as I saw it, I got a flashback from a year ago or so, when the proofs of another paper of mine were sent to me from ApJ, only to realize that that time too "AGN" had magically turned into "AGNs". Back then I explicitly asked the editor to revert it to my original choice of "AGN". The editor disregarded my request and since there is no communication between the author and the editor after the proofs are returned, now there will be "AGNs" in my bibliography for all posterity.

It is quite simple really...AGN stands for Active Galactic Nucleus. What is the plural of that? Active galactic Nuclei. Nuclei! Not Nucleuses! So it's AGN not AGNs. I looked through the ApJ website, their style recommendation for authors, and I couldn't find any specific requirement for the plural of AGN to be AGNs. In any case, once again I kindly asked the editor to revert back to "AGN"...lets see if this time it will work!

A paper looking at the incidence of AGN-driven outflows in a large statistical sample of SDSS Type 2 AGN has just been accepted to the Astrophysical Journal. This paper, which I am a co-author of, builds upon the work of Bae & Woo (2014). In that paper, Hyun-Jin Bae, a graduate student working with Prof. Jong-Hak Woo looked that [OIII] emission line profiles of a large (~23,000) sample of Type 2 AGN from SDSS at redshifts z<0.1, finding strong indications that outflows are common among luminous Type 2 AGN. Woo, Bae, Son, & Karouzos revisit this sample and expand it to higher redshifts (z<0.3) and revise the methodology to identify AGN-driven outflows.

The paper is currently on the arXiv!

We find that outflows are indeed prevalent in Type 2 AGN, with the fraction of AGN showing evidence for outflowing [OIII] gas rapidly increasing with increasing [OIII] luminosity and AGN Eddington ratio. For these AGN, the [OIII] emission profile shows strong asymmetries with respect to the systemic velocity of the galaxy, blueshifted emission, and large dispersions compared to the stellar velocity dispersion of their hosts.

I particularly worked and contributed to the connection between the [OIII] outflows and radio-jets. From a tolal of 39,000 Type 2 AGN, a bit more than 6,000 objects are detected in the radio by the FIRST 1.4 GHz survey. We explored potential links between the peculiar kinematics shown by [OIII] with radio luminosity and radio loudness. It is possible that radio jets can drive outflows in the ionized phase of the gas in these sources. However, we found no clear indication supporting this scenario. Neither the radio luminoisty nor the radio loudness correlates with [OIII] outflow metrics. 

Interestingly, we find a correlation between radio luminosity and [OIII] velocity dispersion, which has been previously discussed in the literature as potential evidence for a link between radio jets and ionized gas outflows. However, there is an underlying correlation of both the radio luminosity and the [OIII] velocity dispersion with the stellar mass and therefore the stellar velocity dispersion. Once this is accounted for, then the correlation between the radio luminosity and the [OIII] velocity dispersion disappears!

We are currently working on several follow-up observations to investigate aspects of these results. We will soon be submitting a series of papers that I am leading to look at the spatially resolved kinematics of some of the best candidates among these 39,000 Type 2 AGN with integral field unit (IFU) spectroscopy. In parallel, I used MMT to look at the ionized gas properties along the extended radio jets of the best candidates among the cross-matched SDSS-FIRST sample. The analysis of these data is ongoing and a paper is in preparation, to be submitted early next year.

Our recent discovery of a z~6 quasar using the Gemini/GMOS instruments was featured on the Gemini website and was also announced in a press release by the Korean Astronomy and Space Institute (KASI). Exciting!

Here is the newspiece: http://www.gemini.edu/node/12446

Today there was a press release about the discovery of a redshift 6 quasar (or roughly when the Universe was just 900 million years old)! The high-z quasar candidate was selected using data from the Infrared Medium-Deep Survey (IMS) and was confirmed using the Gemini GMOS spectrograph. This detection help us put constraints on the re-ionization of the IGM from quasar emission, suggesting that quasars alone may not be enough to re-ionized the Universe.

With Apple stabbing me in the back like Brutus and discontinuing the iWeb application, I finally got around to revamping my old website and migrating to a different platform. New material has been added and everything looks nice and shiny! Roam around and feel free to send me your comments or ideas here.

Our paper on comparing virial black hole mass estimators in the rest-frame UV and optical for high-redshift and low luminosity AGN has been accepted for publication to the Astrophysical Journal. This study is based on near-IR spectra obtained with the FMOS multi-object spectrograph on the 8.2m Subaru telescope! We find that carbon-based virial mass estimates correlate well with Balmer estimators although with larger intrinsic scatter (~0.35 dex) than MgII. We compile a large sample of previous studies on CIV and CIII and use them together with our sample to calibrate the virial factor necessary for calculating black hole masses from the width of the CIII] and CIV emission lines.