Galactic outflows
(Top) Multiwavelength image of a nearby star-forming galaxy, M82.
(Bottom) Multiwavelength emission from a bubble driven by jets from a supermassive black hole.
Galaxies do not evolve as closed systems, and the amount and nature of infall and outflow regulate the crucial aspects of galactic evolution. The movement of gas in and out of a galaxy plays a crucial role in dictating the star formation history of the galaxy, which in turn determines other aspects of its evolution. The infall and outflow of gas also shape the so-called galaxy ecosystem, in the immediate vicinity of the galaxy.
Outflows can be caused by mainly two kinds of energetic sources in the galaxy, first, supernovae and second, supermassive black holes. Individual supernovae (energy 10^{51} erg) quickly lose most of their energy via radiation and do not contain enough energy to drive gas out of the galaxy. However, multiple supernovae, if happen collectively within a short space-time, can drive gas out of the galaxy and thus cause galactic outflow. Similarly, supermassive black holes at the galactic center can release energy in the form of a highly collimated jet or widespread winds, causing galactic outflow.
Although we have some idea of when and how such outflows can be launched from a star-forming region or supermassive black hole, we are still unsure about the specifics. Additionally, the exact nature of the interaction of such outflows with the interstellar medium is not known. My research work involves studying the origin and the effect of such outflows in galaxies.
Some throwback pictures
Galactic outflows due to supernovae activity in a simulated galaxy. The top row shows the density and the bottom row shows the x-ray emission from such outflows.
Image from Vijayn A., Sarkar, K. C., etal. 2018. Link
Outflows created by a highly star forming galaxy. Most of the star formation in such highly star forming galaxies happen at the galactic center. Therefore, the supernovae are highly clustered in space and time. The resulting supernovae energy pushes gas out of the galaxy and can cause a strong outflow. The image shows the density, temperature, and X-ray emissivity in a such an outflow. Read Sarkar K. C., etal 2016 for more details.
Relevant Publications
Dissipation of AGN jets in a clumpy interstellar medium: Dutta R., Sharma P., Sarkar K. C., 2024, Arxiv:2401.00446
Feedback-Free Starbursts at Cosmic Dawn: Observable Predictions for JWST: Li Z., Dekel A., Sarkar K. C., Aung H., Giavalisco M., Mandelker N., Tacchella S., 2023, arXiv, arXiv:2311.14662. doi:10.48550/arXiv.2311.14662
Efficient formation of massive galaxies at cosmic dawn by feedback-free starbursts: Dekel A., Sarkar K. C., Birnboim Y., Mandelker N., Li Z., 2023, MNRAS, 523, 3201. doi:10.1093/mnras/stad1557
Self-ionizing Galactic Winds: Sarkar K. C., Sternberg A., Gnat O., 2022, ApJ, 940, 44. doi:10.3847/1538-4357/ac9835
Extraplanar X-ray emission from disc-wide outflows in spiral galaxies: Vijayan A., Sarkar K. C., Nath B.~B., Sharma P., Shchekinov Y., 2018, MNRAS, 475, 5513. doi:10.1093/mnras/sty198
Diffuse X-Ray Emission from Star-forming Galaxies: Sarkar K. C., Nath B.~B., Sharma P., Shchekinov Y., 2016, ApJL, 818, L24. doi:10.3847/2041-8205/818/2/L24
Long way to go: how outflows from large galaxies propagate through the hot halo gas: Sarkar K. C., Nath B.~B., Sharma P., Shchekinov Y., 2015, MNRAS, 448, 328. doi:10.1093/mnras/stu2760