Sangeeta Malhotra | |
|---|---|
| Education | Delhi University (BA, Physics, 1988) Indian Institute of Technology, Kanpur (M.A., Physics, 1990) Princeton University(Ph.D., 1995) |
| Occupation | Astrophysicist |
Sangeeta Malhotra is an astrophysicist who studies galaxies, their contents, and their effects on the universe around them. The objects she studies range from our own Milky Way galaxy to some of the earliest and most distant known galaxies in the epoch of cosmic dawn.
Malhotra works at the NASA Goddard Space Flight Center, where she is part of the Nancy Grace Roman Space Telescope project. [1] She was previously a tenured full professor at Arizona State University.
Malhotra received her bachelor's degree in Physics from Delhi University in 1988, and her Master's degree in Physics from the Indian Institute of Technology - Kanpur in 1990. In 1995, she became the first woman of color to receive a PhD in Astrophysics from Princeton University. [1] Her Ph.D. supervisor at Princeton was Professor Gillian Knapp. Malhotra's Ph.D. thesis examined the distribution of atomic and molecular gas in the Milky Way galaxy. Results from her thesis work are reproduced in the textbook "Galactic Structure", by Binney and Merrifield. [2]
After completing her Ph.D., Malhotra first held a postdoctoral fellowship at the California Institute of Technology. [1] She next won a NASA Hubble Fellowship, which she held at the National Optical Astronomy Observatory in Tucson and subsequently at the Johns Hopkins University in Baltimore, Maryland. She then joined the science staff at the Space Telescope Science Institute in Baltimore, where she worked from 2001-2005. She moved to a faculty position at Arizona State University in Tempe, Arizona in 2006, where she helped build up the new School of Earth and Space Exploration. [1] She moved to NASA's Goddard Space Flight Center in early 2017 to take up a position working on development of the Nancy Grace Roman Space Telescope.
Malhotra and collaborators used Infrared Space Observatory data to study the far-infrared line emission from galaxies. In particular, she demonstrated that the 158 micron emission line of ionized carbon becomes a relatively less prominent spectral feature in galaxies with higher infrared luminosity and/or warmer interstellar dust. [3] [4]
Malhotra initiated the Large Area Lyman Alpha survey [5] in the late 1990s. This was one of the first research projects to successfully identify galaxies in the early universe using their Lyman alpha emission lines, a method that had been first proposed in 1967 by Bruce Partridge and Jim Peebles. [6] She has gone on to study galaxies with strong Lyman alpha lines in detail. In particular, she demonstrated that they tend to be young, with extreme star formation properties [7] and (for galaxies) small sizes. [8]
She also pioneered the technique of using Lyman alpha galaxies to study cosmological reionization, leading a 2004 paper that demonstrated that the gas between galaxies was already mostly ionized at redshift 6.5, when the universe was less than a billion years old. [9] Recently, she, her former Ph.D. student V. S. Tilvi, and other collaborators identified the most distant galaxy group so far known (EGS77), and found evidence that these galaxies are ionizing their surroundings. [10] [11] She is the US principal investigator of the ongoing multinational LAGER project (Lyman Alpha Galaxies in the Epoch of Reionization), which is identifying hundreds of Lyman alpha galaxies in the epoch of cosmic dawn.
Malhotra has led three Hubble Space Telescope treasury programs [12] (GRAPES, PEARS, and FIGS [13] ) that have collectively advanced the application of slitless spectroscopic observations from space. While initially designed to identify galaxies in the distant universe, [14] [15] [16] these projects have also proven invaluable for identifying galaxies at intermediate distances, [17] studying the chemical compositions of those galaxies, [18] [19] and even studying stars in our own Galaxy. [20] Further developments of these techniques form a core part of the planned observing programs for ESA's Euclid mission and NASA's Roman mission, and Malhotra is helping develop plans for the Roman application.
Malhotra has directed multiple PhD students in studying Green Pea galaxies. She and her collaborators have demonstrated that these comparatively local objects bear striking similarities to Lyman alpha galaxies in the early universe, [21] [22] which is valuable because the pea galaxies are easier to study in detail than their more distant counterparts.[ citation needed ]
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Malhotra has advised over a half dozen Ph.D. thesis students, including Steven Finkelstein, Nimish Hathi, Vithal Tilvi, Lifang Xia, Huan Yang, Tianxing Jiang, and John Pharo. [23]
Malhotra was awarded a NASA Hubble Fellowship in 1998. [24]
She is a Legacy Fellow of the American Astronomical Society. [25]
The Local Group is the galaxy group that includes the Milky Way. It has a total diameter of roughly 3 megaparsecs (10 million light-years; 9×1019 kilometres), and a total mass of the order of 2×1012 solar masses (4×1042 kg). It consists of two collections of galaxies in a "dumbbell" shape; the Milky Way and its satellites form one lobe, and the Andromeda Galaxy and its satellites constitute the other. The two collections are separated by about 800 kiloparsecs (3×106 ly; 2×1019 km) and are moving toward one another with a velocity of 123 km/s. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster. The exact number of galaxies in the Local Group is unknown as some are occluded by the Milky Way; however, at least 80 members are known, most of which are dwarf galaxies.
In the fields of Big Bang theory and cosmology, reionization is the process that caused electrically neutral atoms in the universe to reionize after the lapse of the "dark ages".
A rogue planet is an interstellar object of planetary mass which is not gravitationally bound to any star or brown dwarf. Rogue planets originate from planetary systems in which they are formed and later ejected. They can also form on their own, outside a planetary system. The Milky Way alone may have billions to trillions of rogue planets, a range the upcoming Nancy Grace Roman Space Telescope will likely be able to narrow down.
A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition.
A Lyman-alpha emitter (LAE) is a type of distant galaxy that emits Lyman-alpha radiation from neutral hydrogen.
NGC 4323 is a lenticular or dwarf elliptical galaxy located about 52.5 million light-years away in the constellation Coma Berenices. The galaxy was discovered in 1882 by astronomer Wilhelm Tempel and is a member of the Virgo Cluster.
The thick disk is one of the structural components of about 2/3 of all disk galaxies, including the Milky Way. It was discovered first in external edge-on galaxies. Soon after, it was proposed as a distinct galactic structure in the Milky Way, different from the thin disk and the halo in the 1983 article by Gilmore & Reid. It is supposed to dominate the stellar number density between 1 and 5 kiloparsecs above the galactic plane and, in the solar neighborhood, is composed almost exclusively of older stars. Its stellar chemistry and stellar kinematics are also said to set it apart from the thin disk. Compared to the thin disk, thick disk stars typically have significantly lower levels of metals—that is, the abundance of elements other than hydrogen and helium.
HD 162826 is a star in the constellation Hercules. It is about 110 light-years away from Earth. With an apparent magnitude of 6.55, the star can be found with binoculars or a low-power telescope by reference to nearby Vega in the constellation Lyra.
NGC 3862 is an elliptical galaxy located 300 million light-years away in the constellation Leo. Discovered by astronomer William Herschel on April 27, 1785, NGC 3862 is an outlying member of the Leo Cluster.
Benedetta Ciardi is an Italian astrophysicist.
NGC 708 is an elliptical galaxy located 240 million light-years away in the constellation Andromeda and was discovered by astronomer William Herschel on September 21, 1786. It is classified as a cD galaxy and is the brightest member of Abell 262. NGC 708 is a weak FR I radio galaxy and is also classified as a type 2 Seyfert galaxy.
NGC 703 is a lenticular galaxy located 240 million light-years away in the constellation Andromeda. The galaxy was discovered by astronomer William Herschel on September 21, 1786 and is also a member of Abell 262.
NGC 4636 is an elliptical galaxy located in the constellation Virgo. It is a member of the NGC 4753 Group of galaxies, which is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster. It is located at a distance of about 55 million light years from Earth, which, given its apparent dimensions, means that NGC 4636 is about 105,000 light years across.
NGC 4318 is a small lenticular galaxy located about 72 million light-years away in the constellation Virgo. It was discovered by astronomer John Herschel on January 18, 1828. NGC 4318 is a member of the Virgo W′ group, a group of galaxies in the background of the Virgo Cluster that is centered on the giant elliptical galaxy NGC 4365.
2MASS J11263991−5003550(2MASS J1126−5003) is a brown dwarf about 53 light-years distant from earth. The brown dwarf is notable for an unusual blue near-infrared color. This brown dwarf does not show subdwarf features and the blue color cannot be explained by an unresolved binary. Instead the blue color is explained by patchy clouds. The patchy cloud model allows thick clouds and a cloud coverage of 50% to explain the spectra of 2MASS J1126−5003. Other blue L-dwarfs exist, but are quite rare.
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