RIT: Lifting the veil on a dark galaxy

[MargaritaMc]

When I first glanced at this news release I assumed it was related to this thread, which also treats of Cepheids found through the VISTA programme, but it is a separate piece of research. I haven't yet been able to locate the article in ApJL, but the arXiv version is available.

Rochester Institute of Technology: Lifting the veil on a dark galaxy
PUBLIC RELEASE: 6-FEB-2015 via Eureka
A cluster of young, pulsating stars discovered in the far side of the Milky Way may mark the location of a previously unseen dark-matter dominated dwarf galaxy hidden behind clouds of dust.

A team, led by Sukanya Chakrabarti from Rochester Institute of Technology, analyzed near-infrared data collected by the European Southern Observatory's survey VISTA to find four young stars approximately 300,000 light years away. These young stars are Cepheid variables-"standard candles" that astronomers use to measure distances. According to Chakrabarti, these are the most distant Cepheid variables found close to the plane of the Milky Way. The paper announcing the discovery appears in Astrophysical Journal Letters and is available online.

The stars appear to be associated with a dwarf galaxy Chakrabarti predicted in 2009 based on her analysis of ripples in the Milky Way's outer disk. Chakrabarti's earlier study predicted the location of the dark-matter dominated dwarf galaxy. Radiation emitted by the Cepheid variable stars allowed her to derive accurate distances and test her prediction. Chakrabarti analyzed VISTA's database of tens of millions of stars to find these clustered Cepheid variables in the Norma constellation, all within one degree of each other.

"These young stars are likely the signature of this predicted galaxy," said Chakrabarti, assistant professor in RIT's School of Physics and Astronomy. "They can't be part of our galaxy because the disk of the Milky Way terminates at 48,000 light years."...

Here is the abstract of the arXiv version arXiv:1502.01358 [astro-ph.GA]

Clustered Cepheid Variables 90 kiloparsec from the Galactic Center

Sukanya Chakrabarti, Roberto Saito, Alice Quillen, Felipe Gran, Christopher Klein, Leo Blitz
(Submitted on 4 Feb 2015)

Distant regions close to the plane of our Galaxy are largely unexplored by optical surveys as they are hidden by dust. We have used near-infrared data (that minimizes dust obscuration) from the ESO Public survey VISTA Variables of the Via Lactea (VVV) (Minniti et al. 2011; Saito et al. 2012; henceforth S12) to search for distant stars at low latitudes. We have discovered four Cepheid variables within an angular extent of one degree centered at Galactic longitude of l=−27.4∘ and Galactic latitude of b=−1.08∘. We use the tightly constrained period-luminosity relationship that these pulsating stars obey (Persson et al. 2004; Matsunaga et al. 2011) to derive distances. We infer an average distance to these Cepheid variables of 90 kpc. The Cepheid variables are highly clustered in angle (within one degree) and in distance (the standard deviation of the distances is 12 kpc). They are at an average distance of ∼2 kpc from the plane and their maximum projected separation is ∼1 kpc. These young (∼ 100 Myr old), pulsating stars (Bono et al. 2005) are unexpected at such large distances from the Galactic disk, which terminates at ∼ 15 kpc (Minniti et al. 2011). The highly clustered nature in distance and angle of the Cepheid variables suggests that the stars may be associated with a dwarf galaxy, one that was earlier predicted by a dynamical analysis (Chakrabarti \& Blitz 2009).*

Comments: accepted to ApJL

* MNRAS: Tidal imprints of a dark subhalo on the outskirts of the Milky Way

Margarita

[bystander]

Galaxy Quakes Could Improve Hunt for Dark Matter
Rochester Institute of Technology | 2016 Jan 07

[img3="These images of the Milky Way show the distribution of gas, at left, compared to
the distribution of stars, at right, after the dwarf satellite disrupts the galaxy.
Credit: Sukanya Chakrabarti, Rochester Institute of Technology"]http://www.rit.edu/news/lib/filelib/201 ... llite1.jpg[/img3][hr][/hr]

A trio of brightly pulsating stars at the outskirts of the Milky Way is racing away from the galaxy and may confirm a method for detecting dwarf galaxies dominated by dark matter and explain ripples in the outer disk of the galaxy.

This new method to characterize dark matter marks the first real application of the field of galactoseismology. Just as seismologists analyze waves to infer properties about the Earth’s interior, Sukanya Chakrabarti, assistant professor at Rochester Institute of Technology, uses waves in the galactic disk to map the interior structure and mass of galaxies. She presented her findings at a press conference hosted by the American Astronomical Society meeting in Kissimmee, Fla., on Jan. 7. Chakrabarti’s findings have been submitted to Astrophysical Journal Letters.

Her team used spectroscopic observations to calculate the speed of the three Cepheid variables—stars used as yardsticks to measure distance in galaxies—in the Norma constellation. Chakrabarti’s 2015 study used Cepheid variables to mark the location of a dark-matter dominated dwarf galaxy approximately 300,000 light years away. In contrast, the disk of the Milky Way terminates at 48,000 light years.

The current study tracks a cluster of Cepheids that are racing away at an average speed of 450,000 miles per hour; while the radial velocity of stars in the stellar disk of the Milky Way is about 13,000 miles per hour, Chakrabarti said. The method confirms her 2009 prediction. ...

Dwarf Galaxy Sends Ripples Through Milky Way’s Suburbs: A New Way to Explore Dark Matter
Gemini Observatory | 2016 Jan 07