Scientific Collaborations



I have had the privilege of working with Dr. David Martinez-Delgado ( Heidelberg University, formally of Max-Planck Institute for Astronomy and IAC ), Prof. Andrew C. Fabian ( Institute of Astronomy, University of Cambridge, UK) and international teams of professional astronomers and astrophysicists.

Following is a list of published papers describing their results:


4, January, 2016
New scientific collaboration accepted for publication by the Monthly Notices of the Royal Astronomical Society

Satellite accretion in action: a tidally disrupting dwarf spheroidal around the nearby spiral galaxy NGC 253


We report the discovery of NGC 253-dw2, a dwarf spheroidal galaxy undergoing tidal disruption around a nearby spiral galaxy, NGC 253 in the Sculptor group: the first such event identified beyond the Local Group. The dwarf was found using small-aperture amateur telescopes and followed up with Suprime-Cam on the 8m Subaru Telescope in order to resolve its brightest stars.

Read the full .pdf documentation.

Read more about this discovery at New Scientist, January 4, 2016.
 




13, November, 2015
New scientific collaboration submitted for publication to Astronomy & Astrophysics

DGSAT: Dwarf Galaxy Survey with Amateur Telescopes I. Discovery of 11 low surface brightness systems around nearby spiral galaxies


We introduce the Dwarf Galaxy Survey with Amateur Telescopes (DGSAT) project and report the discovery of eleven Low Surface Brightness galaxies in the fields of the nearby galaxies NGC 2683, NGC 3628, NGC 4594 (M104), NGC 4631, NGC 5457 (M101), and NGC7814. The DGSAT project aims at using the potential of modest telescopes to probe low surface brightness features around large galaxies and to increase the sample size of the dwarf satellite galaxies in the Local Volume. Using long exposure images centred on the parent galaxy, the field of view is explored for extended low surface brightness objects. After identifying dwarf galaxy candidates, their observed properties are extracted by fitting models to their light profiles. This paper reports the discovery of eleven new low surface brightness galaxies in the fields of NGC 2683, 3628, 4594, 4631, 5457, and 7814, respectively.

Our contribution to this investigation was the dicovery of satellite galaxies around NGC 4631 (the Whale galaxy).

Read the full .pdf documentation.

 




18, September, 2015
New scientific collaboration published by the Astrophysical Journal

Discovery of a stellar tidal stream and new satellite galaxies around the Whale galaxy, NGC 4631


We report the discovery of a stellar tidal stream in the halo of the familiar Whale galaxy (NGC4631), a nearby edge-on spiral interacting with NGC4656, also known as the Hockey Stick galaxy. The stream has two components: a bridge-like feature extended between NGC4631 and NGC4656 and an overdensity with extended features on the opposite side of the NGC4631 disk. The orientation of the southern portion of the stream relative to the orientations of NGC4631 and NGC4656 is not consistent with an origin from interaction between these two spirals, and is more likely debris from a minor merger with a former dwarf satellite.

Our deep images also detected the presence of two overdensities. Their morphology is consistent with that of faint, extended dwarf galaxy satellites of NGC 4631. A third galactic satellite candidate was subsequently confirmed in a separate investigation conducted by B. Javanmardi, D. Martinez-Delgado, et al.

Read the full .pdf documentation.

Read more about this discovery in the AAS Nova Journal, October 19, 2015.
 




1, August, 2014
New scientific collaboration published by the Astrophysical Journal

Cannibalization and rebirth in the NCG 5387 system. I. The stellar stream and star-forming region


We have identified a low surface brightness stellar stream from visual inspection of Sloan Digital Sky Survey (SDSS) imaging for the edge-on spiral galaxy NGC 5387. An optically blue overdensity coincident where the stream intersects with the disk of NGC 5387 was also identified in SDSS data and in the Galaxy Evolution Explorer Deep Imaging Surve. It contributes 38% of the total far-UV integrated flux from NGC 5387. Deeper optical imaging was acquired with the Vatican Advanced Technology Telescope that confirmed the presence of both features.

Spectroscopy determined the blue overdensity shares the same redshift as NGC 5387, consists of young stellar populations, is metal-poor and is forming stars at a furious rate of over 1-3 million per year. The most likely interpretations are that the blue overdensity is (1) a region of enhanced star formation in the outer disk of NGC 5387 induced by the minor accretion event or (2) the progenitor of the stellar stream experiencing enhanced star formation.

Read the full .pdf documentation.
 




30, June, 2014
New scientific collaboration published by the Monthly Notices of the Royal Astronomical Society

Kinematics and simulations of the stellar stream in the halo of the Umbrella Galaxy


We study the dynamics of faint stellar substructures around the Umbrella Galaxy, NGC 4651, which hosts a dramatic system of streams and shells formed through the tidal disruption of a nucleated dwarf elliptical galaxy. We elucidate the basic characteristics of the system (colours, luminosities, stellar masses) using multi-band Subaru/Suprime-Cam images.

We identify candidate kinematic tracers (globular clusters, planetary nebulae, Hii regions), and follow up a subset with Keck/DEIMOS spectroscopy to obtain velocities. We find 15 of the tracers are likely associated with halo substructures, including the probable stream progenitor nucleus.

We model the stream using single test-particle orbits, plus a rescaled pre-existing N-body simulation.

We infer a very eccentric orbit with a period of ~0.35 Gyr and turning points at ~2- 4 and~40 kpc, implying a recent passage of the satellite through the disc, which may have provoked the visible disturbances in the host galaxy.

This work confirms that the kinematics of low surface brightness substructures can be recovered and modelled using discrete tracers- a breakthrough that opens up a fresh avenue for unraveling the detailed physics of minor merging.

Read the full .pdf documentation.
 




9, December, 2011
New scientific collaboration published in the Astrophysical Journal Letters

Dwarfs gobbling dwarfs: a tidal star stream around NGC 4449


We have mapped and analyzed a stellar stream in the halo of the nearby dwarf starburst galaxy NGC 4449, detecting it in deep integrated-light images using the Black Bird II Observatory 0.5-meter telescope, and resolving it into a river of individual red giant branch stars using the 8.2-meter Subaru/Suprime-Cam (NAOJ). The properties of the stream imply a massive dwarf spheroidal progenitor, which will continue to disrupt and deposit an amount of stellar mass that is comparable to the existing stellar halo of the main galaxy. The ratio between luminosity or stellar-mass between the two galaxies represents a stealth major merger. This singular discovery also suggests that satellite accretion can play a significant role in building up the stellar halos of low-mass galaxies, and possibly in triggering their starbursts.

Read the full .pdf documentation.
 




11, November, 2011
New scientific collaboration published in the Astrophysical Journal Letters

The formation of shell galaxies similar to NGC 7600 in the cold dark matter cosmogony

A new N-body simulation, demostrates the continuous accretion of stars and dark matter clumps can create a swath of diffuse circumgalactic structures. The disruption of a massive near-radial orbiting dark matter clump creates a complex system of transient concentric shells which bare a striking resemblance to those observed surrounding NGC 7600. With the aid of the simulation we interpret NGC 7600 in the context of the CDM model.

Read the full .pdf documentation.
 




17, October, 2011
New scientific collaboration published in the Astronomical Journal

Discovery of a Stellar Tidal Stream in the Halo of Messier 63 (NGC 5055)


The results of a collaboration spanning several years regarding the existance of a stellar stream surrounding Messier 63 (NGC 5055) has been published by the Astronomical Journal. Click here for the full pdf documentation.
 




25, May, 2011
New scientific collaboration submitted to Monthly Notices of the Royal Astronomical Society (MNRAS)

A wide Chandra view of the core of the Perseus cluster



An international team of professional astronomers, led by Prof. Andrew C. Fabian ( Institute of Astronomy, University of Cambridge, UK) has submitted a new paper for publication featuring new Chandra images of the X-ray emission from the core of the Perseus cluster of galaxies. This image and a description about its data acquisition and final production were included.

Download the PDF document.
 




15, May, 2011
New scientific collaboration published

Good Science with Modest Instruments

Download the PDF document.

Presented on May 23, 2011 at the Society of Astronomical Sciences Symposium in Big Bear Lake, California, this paper summarizes the benefits of conducting astronomical research with off the shelf equipment and a motivated team of professionals and amateurs. This paper was written in collaboration with Dr. David Martinez-Delgado, MPIA.
 




7, September, 2010
Max-Planck Institute for Astronomy

Spirals eat dwarfs: Galactic tendrils shed light on evolution of spiral galaxies


Read the press release here and news items based on the release that appear in National Geographic News, Universe Today and Space.com

Read the article about this project here.
 




2, April, 2010
Astronomical Journal, Volume 140, Number 4

Stellar Tidal Streams in Spiral Galaxies of the Local Volume: A Pilot Survey with Modest Aperture Telescopes


See the full color image. Click here for the full article text in PDF format.
 




26, March, 2010
Astronomy & Astrophysics

A Multi-wavelength analysis of M81 (NGC3031): insight on the nature of Arpís loop


See the full color image. Click here for the full article text in PDF format.
 




10, October, 2009
Astrophysical Journal

Unveiling the Nature of M94ís Outer Region: a Panchromatic Perspective


See the full color image. Click here for the full article text in PDF format.

 




20, February 2009
Astrophysical Journal

Discovery of a Giant Stellar Tidal Stream Around the Disk Galaxy NGC4013


See the full color image. Click here for the full article text in PDF format.




10, December 2008
Astrophysical Journal

The ghost of a dwarf galaxy: fossils of the hierarchical formation of the nearby spiral galaxy NGC5907


See the full color image. Click here for the full article text in PDF format.





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