A TIDALLY DISRUPTING DWARF SPHEROIDAL AROUND THE GALAXY NGC 253

Image: Spiral galaxy NGC 253 Credit: Robert Gendler/Jim Mistin

The modern paradigm of cold dark matter with a cosmological constant (ΛCDM) predicts that galaxies form hierarchically - growing through the gradual merging of many smaller galaxies.

A giant spiral like our Milky Way is expected to undergo a succession of dwarf galaxy accretion events which have different observational signatures, depending on their occurrence in the past, present, or future. Ancient accretion events can be detected through careful sifting of the chemodynamical phase-space of halo stars. Ongoing accretion is implied by the presence of satellite galaxies within the halo, and imminent accretion is marked by the existence of field dwarfs near to their future hosts.

Left: Amateur images of NGC 253 and its satellite NGC 253-dw2.
The field of view is of ~ 67 x 60 kpc. North is up and East is left.
The zoom-in on NGC 253-dw2 covers ~ 8 x 7 kpc.
Right: Subaru/Suprime-Cam image.
Credit: Romanowsky, Martinez-Delgago et. al 2016

Some researchers (Romanowsky, Martinez-Delgago et. al 2016) report the discovery of NGC 253-dw2, a dwarf spheroidal (dSph) galaxy candidate undergoing tidal disruption around a nearby spiral galaxy NGC 253 in the Sculptor group: the first such event identified beyond the Local Group. it is noteworthy that the dwarf was found using small-aperture amateur telescopes, and followed up with Suprime-Cam on the 8 m Subaru Telescope in order to resolve its brightest stars.

The morphological properties of NGC 253-dw2 mark it as distinct from normal dSphs and imply ongoing disruption at a projected distance of ~ 50 kpc from the main galaxy. Their observations support the hierarchical paradigm wherein massive galaxies continously accrete less massive ones, and provide a new case study for dSph infall and dissolution dynamics.

The paper (Romanowsky, Martinez-Delgago et. al 2016) is available online and is published in the MNRAS. >>
http://mnrasl.oxfordjournals.org/content/457/1/L103.full.pdf
http://arxiv.org/pdf/1512.03815v2.pdf

Comments

ORBITAL PERIODS OF THE PLANETS

For orbital period generally we refer to the sidereal period, that is the temporal cycle that it takes an object to make a full orbit, relative to the stars. This is the orbital period in an inertial (non-rotating) frame of reference (365,25 days for the earth).

NEW MACRONOVA'S MODEL

Image: The sequence illustrates the macronova model for the formation of a short-duration gamma-ray burst. 1. A pair of neutron stars in a binary system spiral together. 2. In the final milliseconds, as the two objects merge, they kick out highly radioactive material. This material heats up and expands, emitting a burst of light called a macronova. 3. The fading fireball blocks visible light but radiates in infrared light. 4. A remnant disk of debris surrounds the merged object, which may have collapsed to form a black hole Credit: NASA, ESA, and A. Feild (STScI) A macronova (also called a 'kilonova' or an 'r-process supernova' ) occurs when two neutron stars or a neutron star and a black hole merge. It is a near-infrared/optical transient powered by the radioactive decay of heavy elements synthesized in the ejecta (~10 -4 -10 -1 M sun with velocities ~ 0.1-0.3c) of a compact binary merger. Strong electromagnetic radiation is emitted due to the decay of h

Antares overlooking an Auxiliary Telescope

Credit: ESO/B. Tafreshi Brilliant blue stars litter the southern sky and the galactic bulge of our home galaxy, the Milky Way, hangs serenely above the horizon in this spectacular shot of ESO’s Paranal Observatory. This image was taken atop Cerro Paranal in Chile, home to ESO’s Very Large Telescope (VLT). In the foreground, the open dome of one of the four 1.8-metre Auxiliary Telescopes can be seen. The four Auxiliary Telescopes can be utilised together, to form the Very Large Telescope Interferometer (VLTI). The plane of the Milky Way is dotted with bright regions of hot gas. The very bright star towards the upper left corner of the frame is Antares — the brightest star in Scorpius and the fifteenth brightest star in the night sky. Text Credit: ESO Resources Antares overlooking an Auxiliary Telescope Next Post Small Asteroid or Comet 'Visits' from Beyond the Solar System

SpaceTime

Search This Blog