Red Geysers in MaNGA: New Evidence for AGN Maintenance Mode Feedback

(This is a guest post by Edmond Cheung at the Kavli IPMU)

While there have been many recent studies addressing how galaxies shut off, or quench, their star formation, an equally interesting yet relatively unstudied question is how these quenched galaxies remain quenched. This is interesting because these quiescent galaxies often contain gas (from stellar mass loss or mergers) that—if left unimpeded—should cool and form stars. But since we know that quiescent galaxies have not formed a significant amount of stars since they’ve been quenched, there must be something that prevents this gas from cooling.

In the new study by Cheung et al. 2016, Nature, 533, 504, this ‘something’ has been found. Using the ongoing SDSS IV MaNGA survey, which takes resolved spectroscopy for 10,000 nearby galaxies, Cheung et al. discovered a new class of quiescent galaxies—dubbed “red geysers”—that hosts outflowing winds powerful enough to heat ambient gas and suppress future star formation. These winds are manifested in bisymmetric emission features (in H-alpha, [OII], and other strong lines) and are likely powered by their weakly-accreting supermassive black holes.

To highlight the key characteristics of this class, Cheung et al. focus on a prototypical red geyser, which they nicknamed “Akira”—a reference to the critically-acclaimed manga comic of the same name, and in homage to the MaNGA survey and the lead author’s current institute in Japan (Kavli IPMU). Akira is undergoing a minor interaction with another galaxy, which they’ve nicknamed “Tetsuo”—another character in the same manga comic as Akira; the SDSS image of the interaction is shown in panel a of the figure below, which is reproduced from the Cheung et al. 2016. According to merger simulations, Tetsuo is depositing cool gas into Akira, which is detected in redshifted Na D absorption (panels d and e). The expected star-formation from this cool gas, however, is absent: Cheung et al. find that the measured star-formation rate of Akira is much lower than what is expected given the amount of cold gas present. Thus something is prohibiting star formation in Akira—what is it?

The image and diagnostic diagrams of  "Akira", a prototypical red geyser.

The images and diagnostic diagrams of “Akira”, a prototypical red geyser. 

Inspecting the ionized gas properties of Akira, Cheung et al. find an interesting bisymmetric emission pattern in H-alpha and other strong emission lines (panel c). These emission patterns roughly align with the ionized gas velocity gradient (panel h), suggestive of an outflow. To prove that the ionized gas is in an outflowing wind instead of in a rotating disk, Cheung et al. had to disprove the latter case. Using the stellar dynamics of Akira (panels f and g), they obtain a tight constraint on its gravitational potential, from which they are able to predict the ionized gas kinematics in the case of a regularly rotating disk. They find that the observed ionized gas kinematics are significantly higher than the predicted ionized gas kinematics (panel j), indicating that the ionized gas is not under the influence of gravity alone.

Ruling out the disk interpretation, Cheung et al. developed a qualitative wind model that reproduces many of the features of the data, including the ionized gas velocity field and the ionized gas velocity dispersion field. They theorize that this outflowing wind is likely powered by the weakly-accreting supermassive black hole at the center of Akira, which is detected as a central radio point source in the FIRST survey and in followup Jansky VLA observations. They calculate that the energetic output from this low-luminosity active galactic nuclei (AGN) is sufficient to power this outflowing wind, which in turn, has enough energy to counterbalance the cooling of both the warm and cool gas within Akira, and thereby suppress star formation.

While Akira is an ideal case-study, perhaps the most exciting aspect of this study is the fact that there are many more red geysers. Red geysers make up about 10% of quiescent galaxies at moderate stellar masses (2×1010 solar masses), which could have important implications on the duty cycle of this kind of supermassive black hole feedback. Moreover, because they are relatively common, red geysers may exemplify how typical quiescent galaxies maintain their quiescence.

A Fundamental Constant of Nature through the SDSS — Una constante fundamental de la Naturaleza a través del SDSS

(The following is a guest post by Franco Albareti, a PhD candidate at Universidad Autónoma de Madrid. It is based on recent work with co-workers Johan Comparat and Francisco Prada, which was published last year in the Monthly Notices of the Royal Astronomical Society.)

The physical models we use to describe the world around us and predict new phenomena have some free parameters or constants. These parameters must be adjusted to what is experimentally observed. Among them, those known as the fundamental constants of Nature play a central role in our theoretical understanding of physics.

Los modelos físicos que usamos para describir el mundo a nuestro alrededor y predecir nuevos fenómenos contienen parámetros o constantes sin determinar. Estos parámetros deben ajustarse según lo que se observa experimentalmente. Entre ellos, aquellos conocidos como las constantes fundamentales de la Naturaleza desempeñan un papel fundamental en nuestra comprensión teórica de la Física.

In particular, the fine-structure constant (informally called “α”) tells us the strength of electromagnetic interactions. These interactions are responsible for most of the natural phenomena around us. The correct understanding and description of how they work is not only one of the major achievement of science, but had a tremendous impact on modern life, for instance in telecommunications. The BOSS cosmological survey, one of the surveys within SDSS, has constrained the time variation of the fine-structure constant or, alternatively, the strength of the electromagnetic interactions over more than half the age of our Universe (7 Gyrs).

En particular, la constante de estructura fina (para los amigos, “α”) nos da información sobre la fuerza de las interacciones electromagnéticas. Estas interacciones son responsables de la mayoría de los fenómenos naturales que nos rodean. El hecho de que seamos capaces de entender y describir correctamente cómo funcionan, no sólo es uno de los grandes hitos de la Ciencia, sino que también ha tenido un impacto radical en nuestra forma de vida, por ejemplo, en las telecomunicaciones. El cartografiado cosmológico BOSS, uno de los cartografiados que forman parte del SDSS, ha restringido la variación temporal de la constante de estructura fina o, en otras palabras, la fuerza de las interacciones electromagnéticas durante un período de tiempo que abarca más de la mitad de la edad del Universo (7 Ga).

Any change in the fine-structure constant value will leave its imprint on the separation between two characteristic spectral lines of oxygen, see figure 1 below. These lines are emitted by quasars (extremely luminous galaxies whose light reaches us from the furthest places in the Universe). Thus, a bigger or smaller separation between those lines means that the electromagnetic interactions were stronger or weaker when the light was emitted.

Cualquier cambio en el valor de la constante de estructura fina afectará la separación entre dos líneas espectrales del Oxígeno (ver figura 1). Estas líneas son emitidas por cuásares (galaxias extremadamente luminosas cuya luz nos llega desde los lugares más recónditos de nuestro Universo). Una separación mayor o menor entre estas líneas espectrales significa que las interacciones electromagnéticas eran más fuertes/débiles cuando la luz fue emitida.

Doubly-ionized oxygen lines [OIII] observed in a BOSS quasar spectrum. Líneas espectrales de Oxígeno doblemente ionizado [OIII] observadas en un espectro de un cuásar tomado por BOSS.

Figure 1. Doubly-ionized oxygen lines [OIII] observed in a BOSS quasar spectrum.
Líneas espectrales de Oxígeno doblemente ionizado [OIII] observadas en un espectro de un cuásar tomado por BOSS.

Members of the SDSS collaboration have concluded that the value of the fine-structure constant has remained the same over the last 7 billions years in 1 part in 50,000 (figure 2). For this, more than 10,000 quasar spectra collected by BOSS were used (figure 3).

Miembros de la Colaboración SDSS han concluido que el valor de la constante de estructura fina no ha variado durante los últimos 7 mil millones de años en más de una parte en 50.000 (figura 2). Para ello. más de 10.000 espectros de cuásares tomados por BOSS han sido analizados (figura 3).

Measurements of the variation of the fine-structure constant (Δα/α) as a function of redshift (left panel) and line intensity (right panel). The grey bands in the left figure indicate regions where the sky contamination is strong and, therefore, it affects the measured value. Medidas de la variación de la constante de estructura fina (Δα/α) en función del corrimiento al rojo (imagen izquierda) y la intensidad de las líneas (imagen derecha). Las bandas grises en la figura de la izquierda indican las regiones donde la emisión del cielo es fuerte y, por tanto, afecta al valor medido.

Figure 2. Measurements of the variation of the fine-structure constant (Δα/α) as a function of redshift (left panel) and line intensity (right panel). The grey bands in the left figure indicate regions where the sky contamination is strong and, therefore, it affects the measured value.
Medidas de la variación de la constante de estructura fina (Δα/α) en función del corrimiento al rojo (imagen izquierda) y la intensidad de las líneas (imagen derecha). Las bandas grises en la figura de la izquierda indican las regiones donde la emisión del cielo es fuerte y, por tanto, afecta al valor medido.

Figure 3. Left panel: Composite image with all the BOSS quasar spectra used in this research (10,363) sorted by redshift (each horizontal line is a quasar spectrum). The displacement of the spectral lines to larger wavelengths (effect known as redshift) is due to the cosmological expansion of the Universe. Right panel: Composite image centered on the Oxygen lines and horizontally displaced to account for the redshift effect. Imagen izquierda: Conjunto de todos los espectros tomados por BOSS que han sido usados en la investigación (10.363) ordenados según el corrimiento al rojo (cada línea horizontal es un espectro de un cuásar). El desplazamiento de las líneas espectrales hacia longitudes de onda más largas (efecto conocido como corrimiento al rojo) es debido a la expansión cosmológica del Universo. Imagen derecha: Misma imagen anterior centrada en las líneas de Oxígeno y corrigiendo el desplazamiento horizontal para tener en cuenta el corrimiento al rojo.

Figure 3. Left panel: Composite image with all the BOSS quasar spectra used in this research (10,363) sorted by redshift (each horizontal line is a quasar spectrum). The displacement of the spectral lines to larger wavelengths (effect known as redshift) is due to the cosmological expansion of the Universe. Right panel: Composite image centered on the Oxygen lines and horizontally displaced to account for the redshift effect.
Imagen izquierda: Conjunto de todos los espectros tomados por BOSS que han sido usados en la investigación (10.363) ordenados según el corrimiento al rojo (cada línea horizontal es un espectro de un cuásar). El desplazamiento de las líneas espectrales hacia longitudes de onda más largas (efecto conocido como corrimiento al rojo) es debido a la expansión cosmológica del Universo. Imagen derecha: Misma imagen anterior centrada en las líneas de Oxígeno y corrigiendo el desplazamiento horizontal para tener en cuenta el corrimiento al rojo.

Animation -> The animation below shows an image of a quasar, its full optical spectrum (bottom left), a zoom in the oxygen lines used for the analysis (bottom right), and the measured value of the variation of the fine-structure constant as a function of redshift (top panel). It only displays 200 objects among the >10,000 quasars used for the research. (It starts slow so you can pay attention to all of the information, but then it goes faster)

Animación -> Esta animación muestra una imagen de un cuásar, junto con su espectro en el óptico (parte inferior izquierda), un zoom en las líneas de Oxígeno usadas para el análisis (parte inferior derecha), y el valor medido de la variación de la constante de estructura fina como función del corrimiento al rojo (parte superior). La animación sólo muestra 200 objetos de entre los >10.000 cuásares usados para la investigación. (Empieza despacio para que uno se pueda fijar en toda la información que se muestra, pero luego empieza a ir más rápido.)

alpha_spectra_small

Animation of the measured change in the fine structure constant with cosmic time. You may need to refresh this page to see the animation again.

To reach further in the past, when the Universe was five times younger, a dedicated observational program, APOGEE-Q (APOGEE Quasar Survey), is being developed in order to not only measure a variation on the fine-structure constant, but study supermassive black hole masses and quasar redshifts. This program will use an infrared spectrograph from the APOGEE survey instead of the optical one used by BOSS. This allows us to observe the infrared region of the electromagnetic spectrum, where the oxygen lines emitted by distant quasars are found due to the cosmological expansion of the Universe. It will start to take the first data during 2016.

Para remontarnos todavía más atrás en el tiempo, cuando el Universo era cinco veces más joven, un programa observacional específico, APOGEE-Q: APOGEE Quasar Survey, está siendo desarrollado para, no sólo medir la variación de la constante de estructura fina, sino también para estudiar agujeros negros súper masivos y corrimientos al rojo de cuásares. Este programa usará un espectrógrafo infrarrojo del cartografiado APOGEE en vez del espectrógrafo óptico usado por BOSS. Esto nos permitirá observar la región infrarroja del espectro electromagnético, que es donde se encuentran las líneas del Oxígeno emitidas por cuásares muy lejanos debido a la expansión cosmológica del Universo. El programa empezará a tomar los primeros datos en 2016.

P-MaNGA: Emission Lines Properties – Gas Ionisation and Chemical Abundances from Prototype Observations

(The following is a guest post by Francesco Belfiore, a PhD student at Cambridge University’s Kavli Institute for Cosmology, and summarizes his recent paper, which uses preliminary MaNGA data to map gas ionisation in several galaxies.)

Galaxies have long been considered island universes. Ordinarily separated by huge cosmological distances (of the order of millions of light years), most galaxies are not interacting in any visible way with their environment. However, modern theories of galaxy evolution claim otherwise. Starburst galaxies (galaxies which are experiencing a rate of formation of new stars much higher than normal) are known to expel large amounts of ionised (and possibly also neutral) gas towards the intergalactic voids. Supermassive black holes, which we believe to live in the centres of most galaxies, can also give rise to powerful outflows during periods of accretion (when the black hole has “switched on” and is feeding on the surrounding material). Some of these events are violent enough to totally strip a galaxy of its fuel: the gas. Without gas, a galaxy loses its ability to form new stars and becomes progressively older. In a sense, the galaxy has “died”.

This is not the whole story, however.

Continue reading

Integral Field Spectroscopy 101

As frequent readers know, the SDSS-IV-MaNGA survey plans to obtain spatially-resolved spectra of somewhere in the neighborhood of 10,000 galaxies using a technique called integral-field spectroscopy (or IFS). IFS essentially relies on placing an array of fiber-optic cables over an object of interest in the sky, and using the fiber-optics to pipe the light into a spectrograph, which produces the useful data by breaking up that light into its constituent wavelengths (an easy way you can do this at home is with a glass prism). The array of fibers is nicknamed a “bundle,” which is a pre-packaged grouping of fibers that we know the arrangement, and packaging the fibers allows more observational efficiency, since we don’t have to re-position the telescope to make a measurement of the same galaxy at a slightly different point.

However, the specific design of the fiber bundles is an important problem. Continue reading

The Apache Point Observatory Galactic Evolution Experiment (APOGEE)

The following is a synopsis of the new overview paper describing the APOGEE survey. You can find the full paper here.

The first thing to show you about this paper is its authors list. Check out how many contributors there are to this survey:

TitleAuthors

This, together with its length (50 pages) and number of figures (38!!) may give you some idea of the huge scope of the project. To help us sift through it, here is the executive summary, from the APOGEE Principal Investigator, Steven Majewski:

“This paper gives a broad overview of the motivations, design and execution of the APOGEE survey — a synopsis of how the survey was structured and why.”

This isn’t just a technical overview of the survey, however. Says Majewski:

“The most fun part of this new overview paper — a part for which the entire APOGEE team can be justly proud — is the summary of what the project managed to accomplish in such a relatively short amount of time.”

Here are some examples of what he means:

  • 13 technical papers on subjects like spectrograph design, target selection, data reduction, stellar parameter determination, and collaborations with other surveys
  • Uses of time series spectral data for projects as diverse as spectroscopic binary characterization and circumstellar variations around hot stars
  • Detailed maps of stellar radial velocities and metallicities across the Milky Way

It should be mentioned that APOGEE was made possible by a unique 300-fiber-fed, high resolution spectrograph working in the infrared H-band. Hence, thirteen technical papers, while a seemingly large number, were all necessary because APOGEE truly broke ground in a number of ways, both scientific and technical. The actual construction was accomplished by the APOGEE instrument team led by John Wilson (Instrument Scientist) and Fred Hearty (Project Manager).

The detailed maps mentioned in the last bullet deserve a couple of images — they’re too cool not to show. In Figure 24 from the paper, the velocities of stars relative to the Sun are shown against an artist’s impression of the Milky Way Galaxy. Notice how there are clear areas where stars are approaching us, co-moving with us, and moving away from us:

Fig24_RVs

Figure 25 is a similar plot, but showing instead the chemical composition (metal content with respect to hydrogen) in stars across the same survey area. Check out the clear gradient from low-metallicity stars near the edge of the Milky Way’s disk to high-metallicity stars near the Galactic Center:

Fig25_MH

The general trends shown here are not new; instead, it is APOGEE’s unprecedented detail that makes it the biggest kid on the Galactic evolution block. To put APOGEE into context for us, here is Ricardo Schiavon, the APOGEE Survey Scientist, to sum it up:

“APOGEE has, for the first time, provided a homogeneous database of high quality, high resolution infrared spectra for 150,000 stars, which together offer a rigorously systematic spectroscopic census of our home galaxy. Because of it’s unique infrared sensitivity and ability to punch through the blankets of obscuring Galactic dust in its most crowded regions, APOGEE is unveiling the chemical and kinematical properties of stars in parts of the Milky Way never before probed in such exquisite detail. It is a groundbreaking experiment.”

To put it more bluntly: no one has ever done an infrared survey of Milky Way stars in this way.

Undergraduates use SDSS Data to Discover the Densest Galaxies Known

Two undergraduates at San José State University have used public SDSS data to discover two galaxies that are the densest known. Similar to ordinary globular star clusters but a hundred to a thousand times brighter, the new systems have properties intermediate in size and luminosity between galaxies and star clusters.

The first system discovered by the investigators, M59-UCD3, has a width two hundred times smaller than our own Milky Way Galaxy and a stellar density 10,000 times larger than that in the neighborhood of the Sun. For an observer in the core of M59-UCD3, the night sky would be a dazzling display, lit up by a million stars. The stellar density of the second system, M85-HCC1, is higher still: about a million times that of the Solar neighborhood. Both systems belong to the new class of galaxies known as ultracompact dwarfs (UCDs).

The study, led by undergraduates Michael Sandoval and Richard Vo, used imaging data from the Sloan Digital Sky Survey, the Subaru Telescope, and Hubble Space Telescope, as well as spectroscopy from the Goodman Spectrograph on the Southern Astrophysical Research Telescope (SOAR), located on the Cerro Tololo Inter-American Observatory site. The National Optical Astronomy Observatory (NOAO) is a SOAR partner. The SOAR spectrum was used to show that M59-UCD3 is associated with a larger host galaxy, M59, and to measure the age and elemental abundances of the galaxy’s stars.

Two ultra-dense galaxies (insets) have been discovered orbiting larger host galaxies. The compact systems are thought to be the remnants of once normal galaxies that were swallowed by the host, a process that removed the fluffy outer parts of the systems, leaving the dense centers behind. Image credit: A. Romanowsky (SJSU), Subaru, Hubble Legacy Archive

Two ultra-dense galaxies (insets) have been discovered orbiting larger host galaxies. The compact systems are thought to be the remnants of once normal galaxies that were swallowed by the host, a process that removed the fluffy outer parts of the systems, leaving the dense centers behind. Image credit: A. Romanowsky (SJSU), Subaru, Hubble Legacy Archive

 

 

“Ultracompact stellar systems like these are easy to find once you know what to look for. However, they were overlooked for decades because no one imagined such objects existed: they were hiding in plain sight”, said Richard Vo. “When we discovered one UCD serendipitously, we realized there must be others, and we set out to find them.”

The students were motivated by the idea that all it takes to initiate a discovery is a good idea, archival data, and dedication. The last element was critical, because the students worked on the project on their own time. Aaron Romanowsky, the faculty mentor and coauthor on the study, explained, “The combination of these elements and the use of national facilities for follow up spectroscopy is a great way to engage undergraduates in frontline astronomical research, especially for teaching universities like San José State that lack large research budgets and their own astronomical facilities.”

The nature and origins of UCDs are mysterious – are they the remnant nuclei of tidally stripped dwarf galaxies, merged stellar super-clusters, or genuine compact dwarf galaxies formed in the smallest peaks of primordial dark matter fluctuations?

Michael Sandoval favors the tidally stripped hypothesis. “One of the best clues is that some UCDs host overweight supermassive black holes. This suggests that UCDs were originally much bigger galaxies with normal supermassive black holes, whose fluffy outer parts were stripped away, leaving their dense centers behind. This is plausible because the known UCDs are found near massive galaxies that could have done the stripping.”

An additional line of evidence is the high abundance of heavy elements such as iron in UCDs. Because large galaxies are more efficient factories to make these metals, a high metal content may indicate that the galaxy used to be much larger.

To test this hypothesis, the team will investigate the motions of stars in the center of M59-UCD3 to look for a supermassive black hole. They are also on the hunt for more UCDs, to understand how commonly they occur and how diverse they are.

Reference:

“Hiding in plain sight: record-breaking compact stellar systems in the Sloan Digital Sky Survey,” Michael A. Sandoval, Richard P. Vo, Aaron J. Romanowsky et al. 2015, Astrophysical Journal Letters, 808, L32. (Preprint: http://arxiv.org/abs/1506.08828)


 

This post is copied from a press release from the National Optical Astronomy Observatory.

NOAO is operated by Association of Universities for Research in Astronomy Inc. (AURA) under a cooperative agreement with the National Science Foundation.

Discovering Supernova in SDSS Galaxy Spectra

The post below was contributed by Dr. Or Graur, an assistant research scientist at New York University and research associate at the American Museum of Natural History. He recently led a paper based on supernovae detected in SDSS galaxy spectra (published in the Monthly Notices of the Royal Astronomical Society; the full text is available at: http://adsabs.harvard.edu/abs/2015MNRAS.450..905G).

 paper_header

One of the great things about the SDSS is that it can be used in ways that its creators may never have envisioned. The SDSS collected ~800,000 galaxy spectra. As luck would have it, some of those galaxies happened to host supernovae, the explosions of stars, inside the area covered by the SDSS spectral fiber during the exposure time. These supernovae would then “contaminate” the galaxy spectra. In Graur & Maoz (2013), we developed a computer code that allowed us to identify such contaminated spectra and tweeze out the supernovae from the data. In Graur et al. (2015), we used this code to detect 91 Type Ia and 16 Type II supernovae.

 

GM13_method

A galaxy+supernova model (blue) fits the SDSS spectrum (grey) much better than a galaxy-only model (green). The residual spectrum (lower panel, grey), after subtracting the galaxy component, is best-fit by a Type Ia supernova template (red).

With these samples, we measured the explosion rates of Type Ia and Type II supernovae as a function of various galaxy properties: stellar mass, star-formation rate, and specific star-formation rate. All of these properties were previously measured by the SDSS MPA-JHU Galspec pipeline.

 

In 2011, the Lick Observatory Supernova Search published a curious finding: the rates of all supernovae, normalized by the stellar mass of their host galaxies, declined with increasing stellar mass (instead of being independent of it; Li et al. 2011b). We confirmed this correlation, showed that the rates were also correlated with other galaxy properties, and demostrated that all these correlations could be explained by two simple models.

 

Type Ia supernovae, which are thought to be the explosions of carbon-oxygen white dwarfs, follow a delay-time distribution. Unlike massive stars, which explode rather quickly after they are born (millions of years, typically), Type Ia supernovae take their time – some explode soon after their white dwarfs are formed, while others blow up billions of years later. We showed that this delay-time distribution (best described as a declining power law with an index of -1), coupled with galaxy downsizing (i.e., older galaxies tend to be more massive than younger ones), explained not only the correlation between the rates and the galaxies’ stellar masses, but also their correlations with other galaxy properties.

sim_mass_fit

Type Ia supernova rates as a function of galaxy stellar mass

sim_sSFR_fit

Type Ia supernova rates as a function of specific star formation rate.

Simulated rates, based on a model combining galaxy downsizing and the delay-time distribution, are shown as a grey curve on both the above plots. This model is fit to the rates as a function of mass and then re-binned and plotted on the specific star formation rate plot, without further fitting.

For Type II supernovae, which explode promptly after star formation, the correlations are easier to explain; they are simply dependent on the current star-formation rates of the galaxies: the more efficient the galaxy is at producing stars, the more efficient it will be at producing Type II supernovae.

All of the supernova spectra from Graur & Maoz (2013) and Graur et al. (2015) are publicly available from the Weizmann Interactive Supernova data REPository (http://wiserep.weizmann.ac.il/). Please note that their continuua may be warped by our detection method (for details, see section 3 of Graur & Maoz 2013).

The SDSS Reverberation Mapping Project

The below post was contributed by Dr. Catherine Grier, a postdoctoral researcher at Penn State University (formerly a graduate student from Ohio State University, and the Director of the OSU Planetarium) who has led a recent paper based on results from the SDSS Reverberation Mapping Project (accepted for publication in the Astrophysical Journal; the full text is available at: arXiv:1503.030706 Screen Shot 2015-05-21 at 17.16.00 Supermassive black holes (SMBHs) are present in all massive galaxies and are thought to affect the formation and development of the galaxies themselves. Because of this, understanding SMBHs is important in understanding how galaxies are formed and evolve. Observations of quasars are key to understanding SMBHs and how they affect their host galaxies: Quasars are enormously powerful, observable at great distances, and can potentially regulate the growth of their galaxies through their winds, or outflows. We learn about these winds by observing broad absorption line features (BALs; see the diagram below) in quasar spectra that are created by high-speed winds launched from the quasar accretion disk. These winds are made of gas that blocks the light from the quasar and show up as BALs in the spectra of quasars.

Slide1

The CIV region of our target showing the CIV Broad Absorption Line (BAL) features investigated in our study.

These absorption features change throughout time, both in strength and in shape. Under the right conditions, we can use the details of the variability to learn about the density of the absorbing gas and the distance of the gas from the SMBH. This information can sometimes be used to determine if the outflow is powerful enough to affect the star formation in their host galaxy. Previous studies have found that BALs are variable on timescales of several years all the way down to timescales of 8-10 days; however, until now, no studies have reported variability on timescales shorter than 8-10 days. In our recent work, we report on very short-timescale (~1 day) BAL variability observed in a SDSS quasar. The spectra used in our study were taken as a part of the SDSS Reverberation Mapping (SDSS-RM) project using the BOSS spectrograph. We monitored 850 quasars with the BOSS spectrograph from January 2, 2014 through July 3, 2014, resulting in 32 observations over this period. The main goal of the SDSS-RM program is the investigation of the broad emission line regions of quasars, but the targets include a number of quasars hosting BALs and can be used for BAL studies too. During our observing campaign, the equivalent width, or strength, of the highest-velocity CIV BAL feature (see above diagram) changed by over a factor of 2. We did not observe similar variations in either the CIV broad emission line or the overall brightness of the quasar, and the shape of the BAL feature stayed roughly the same during the entire campaign. We observed significant changes in the strength of the BAL on timescales as low as 1.20 days in the quasar rest frame (see the graphs below). This is the shortest time frame ever reported over which significant variability in a BAL trough has been observed.

Slide2

Four different pairs of spectra between which the CIV BAL trough varies significantly.

The most likely cause of the variability is a change in the amount of ionized gas in the outflow. This could be caused by changes in the brightness of the quasar or the amount of energy reaching the absorbing gas for various other reasons. With our observations, we are unable to determine whether this outflow contributes significantly to feedback to the host galaxy, but we do not rule out the possibility. The key to observing this short-term variability was the high cadence of the SDSS-RM campaign, which allowed us to search for BAL variability on shorter timescales than previous studies. This program is still ongoing; we expect to receive more spectra of this target over the next few years with the eBOSS spectrograph, which could shed further light on this topic. The variability properties of this target are similar to those found in other quasars, suggesting that this short-term variability may be common. Further high-cadence spectroscopic campaigns targeting BAL quasars would allow us to learn more about BAL variability in quasars and better understand the possible contributions of BALs to feedback to their host galaxies.