RESEARCH
My research is in studying the properties of diffuse gas in the intergalactic medium and in regions surrounding galxies. For this, I rely on spectroscopic observations. I have made use of optical and ultraviolet spectra of quasars obtained from ground-based facilities like the VLT and Keck telescopes and space based observatories like the Hubble Space Telescope and FUSE satellite. For the last several years, my students and I have been looking at absorption from hydrogen and heavier elements in the low redshift universe to detect gas over a range of temperatures, especially in the 100,000 to a million kelvin. Such gas phase harbors, in the current universe, as much as 40% of the cosmic budget of baryons. We have also been looking at mutliphase properties of gas associated with galaxy clusters and filaments. In addition, we have also used HST far-UV spectra to study outflows from active galactic nuclei.
BARYON CENSUS AT LOW REDSHIFT
Over the nearly 13 billion year history of our universe, only 10% of the total number of baryons (ordinary matter) have collapsed to form structures such as galaxies and galaxy clusters. In other words, galaxy formation has been a relatively inefficient process. Computer simulations of structure formation in a dark energy, dark matter dominated universe suggests that the vast majority of baryons in the nearby universe rests as shock-heated plasma outside of galaxies with temperatures of a million kelvin and densities as low as 1 particle per 100,000 cubic centimeter. Observationally this highly ionized phase of the baryons is just beginning to be discovered. For the last few years, I have been using the Cosmic Origins Spectrograph data to probe environments where these warm-hot baryons might be lurking. On a broader scale, the work adds a level of detail to the ongoing efforts to understand baryonic reservoirs outside of galaxies, and complete the baryon census at low redshift. This work was started, and is being continued, in collaboration with Blair Savage, and Bart Wakker.
Below is an example of the spectroscopic detection of a high baryonic column warm-hot gas associated with a galaxy filament in the low redshift universe.
HIGH METALLICITY GAS CLOUDS OUTSIDE OF GALAXIES
I also work on spectroscopic detections and analysis of high metallicity compact gas clouds outside of the star forming environments of galaxies. The exact origin of such gas clouds were a mystery for a while. Through systematic surveys, using ultraviolet and optical spectra of more than 100 quasars, my collaborators and I produced a large census of such gas clouds over the past 6 billion year history of the universe. Based on the observed number statistics and constraints derived for the ionization modeling we have proposed that a significant population of these gas clouds are supernova enriched or tidally stripped high velocity gas in the extended halos of external galaxies. This work was started, and is being continued, in collaboration with Jane Charlton and Toru Misawa.
OUTFLOWS FROM ACTIVE GALACTIC NUCLEI
More recently, in collaboration with Srianand Raghunathan, Sowgat Muzahid and Vikram Khaire , I have started looking into highly ionized outflows from active galactic nuclei. Accretion of gas by supermassive black holes at the centers of galaxies trigger such outflows. These are thought to considerably influence the evolution of galaxies, particularly their star formation history. Outflows from AGNs are complex in nature, multi-scaled (10 pc - 10 kpc sizes) and multi-phased (10 K - 10 million K). Not all of these have been sufficiently observed or adequately understood. We are interested in finding such outflows in the ultraviolet spectra of AGNs, model them and understand the overall energetics of outflows, and their chemical enrichment.
PUBLICATIONS
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- Pradeep, Jayadev; Narayanan, Anand; Muzahid, Sowgat; Nagai, Daisuke; Charlton, Jane C.; Srianand, Raghunathan. Detection of metal-rich, cool-warm gas in the outskirts of galaxy clusters, 2019, Monthly Notices of the Royal Astronomical Society, 488, 5327   MORE INFO
- Manuwal, A., Narayanan, A., Muzahid, S., Charlton, J. C., Khaire, V., Chand, H. C IV absorbers tracing cool gas in dense galaxy group/cluster environments, 2019, Monthly Notices of the Royal Astronomical Society, 485, 30,   MORE INFO
- Muzahid, S., Fonseca, G., Roberts, A., Rosenwasser, B., Richter, P., Narayanan, A., Churchill, C W., Charlton, J C. COS-Weak: Probing the CGM using analogs of weak Mg II absorbers at z < 0.3, 2018, Monthly Notices of the Royal Astronomical Society, 476, 4965.   MORE INFO
- Narayanan, A., Savage, B. D., Mishra, P. K., Wakker, B. P., Khaire, V., Wadadekar, Y. Detection of Low Metallicity Warm Plasma in a Galaxy Overdensity Environment at z = 0.2, 2018, Monthly Notices of the Royal Astronomical Society, 475, 3529.   MORE INFO
- Pachat, S., Narayanan, A., Khaire, V., Savage, B. D., Muzahid, S., Wakker, B. P. Detection of two intervening Ne VIII absorbers probing warm gas at z = 0.6, 2017, Monthly Notices of the Royal Astronomical Society, Volume 471, Issue 1, 792.   MORE INFO
- Pachat, S., Narayanan, A., Muzahid, S., Khaire, V., Srianand, R., Wakker, B. P., Savage, B. D. A pair of O VI and broad Ly-alpha absorbers probing warm gas in a galaxy group environment at z ~ 0.4, 2016, Monthly Notices of the Royal Astronomical Society, Volume 458, Issue 1, 733.   MORE INFO
- Hussain, T., Muzahid, S.,Narayanan, A., Srianand, R., Wakker, B. P., Charlton, J. C.; Pathak, A. HST/COS detection of a Ne VIII absorber towards PG 1407+265: An unambiguous tracer of collisionally ionized hot gas?, 2015, Monthly Notices of the Royal Astronomical Society, Volume 446, Issue 3, 2444.  MORE INFO
- Muzahid, S., Srianand, R., Arav, N., Savage, B. D.,Narayanan, A.HST/COS Observations of a New Population of Associated QSO Absorbers, 2013, Monthly Notices of Royal Astronomical Society, Volume 431, Issue 3, 2885.  MORE INFO
- Rodriguez Hidalgo, P., Wessels, K., Charlton, J. C.,Narayanan, A., Mshar, A., Cucchiara, A., Jones, T. Evolution of the Population of Very Strong Mg II Absorbers, 2012, Monthly Notices of Royal Astronomical Society, Volume 427, Issue 3, 1801.  MORE INFO
- Muzahid, S., Srianand, R., Savage, B. D.,Narayanan, A., Mohan, V., Dewangan, G. C. Highly Ionized Collimated Outflow from HE0238-1904, 2012, Monthly Notices of Royal Astronomical Society Letters, Volume 424, Issue 1, L59.  MORE INFO
- Savage, B.; Kim, T.-S.; Keeney, B.;Narayanan, A.; Stocke, J.; Wakker, B. P. The Properties of Two Low Redshift O VI Absorbers and Their Associated Galaxies Toward 3C 263, 2012, Astrophysical Journal, Volume 753, Issue 1, 80.  MORE INFO
- Narayanan, A.,Savage, B. D., Wakker, B. P. Cosmic Origins Spectrograph Observations of Warm Intervening Gas at z = 0.325 towards 3C263, 2012, Astrophysical Journal, Volume 752, Issue 1, 65.  MORE INFO
- Savage, B. D., Lehner, N.,Narayanan, A., COS Observations of Metal Line and Broad Lyman-alpha Absorption in the Multi-phase O VI and Ne VIII System at z = 0.20701 toward HE 0226-4110, 2011, Astrophysical Journal, Volume 743, Issue 2, 180.  MORE INFO
- Savage, B. D.,Narayanan, A., Lehner, N., Wakker, B. P., A Multiphase Absorber Containing O VI and Broad H I Directly Tracing Million Kelvin Plasma at Low Redshift Toward HE 0153-4520, 2011, Astrophysical Journal, Volume 731, Issue 1, 14.  MORE INFO
- Narayanan, A., Savage, B. D., Wakker, B. P., Danforth, C. W., Yao, Y., Keeney, B. A., Shull, J. M., Sembach, K. R., Froning, C. S., Green, J. C., 2011, Astrophysical Journal, Volume 730, Issue 1, 15.  MORE INFO
- Narayanan, A., Wakker, B. P., Savage, B. D., Keeney, B. A., Shull, J. M., Stocke, J. T., & Sembach, K. R., Cosmic Origins Spectrograph and FUSE Observations of T ~ 100,000 K Gas In A Nearby Galaxy Filament, 2010, Astrophysical Journal, Volume 721, Issue 2, pp. 960 - 974.  MORE INFO
- Savage, B. D.,Narayanan, A., Wakker, B. P., Stocke, J. T., Keeney, B. A., Shull, J. M., Sembach, K. R., Yao, Y., & Green, J. C., O VI Absorbers Tracing Hot Gas Associated with a Pair of Galaxies at z = 0.167, 2010, Astrophysical Journal, Volume 719, Issue 2, pp. 1526-1545.  MORE INFO
- Narayanan, A., Savage, B. D., Wakker, B. P., Highly Ionized Plasma in the Halo of a Luminous Spiral Galaxy Near z = 0.225, 2010, Astrophysical Journal, Volume 712, Issue 2, pp. 1443 - 1460.  MORE INFO
- Narayanan, A., Wakker, B. P., & Savage, B. D., Detection of Ne VIII in a Multi-phase Intergalactic System Towards 3c 263, 2009, Astrophysical Journal, Volume 703, Issue 1, pp. 74-80.  MORE INFO
- Cucchiara, A., Jones, T., Charlton, J. C., Fox, D. B., Einsig, D., &Narayanan, A.Testing the Possible Intrinsic Origin of the Excess Very Strong Mg II Absorbers Along Gamma-Ray Burst Lines-of-Sight, 2009, Astrophysical Journal, Volume 697, Issue 1, pp. 345-360  MORE INFO
- Narayanan, A., Charlton, J. C., Misawa, T., Green, R. E., & Kim, T-S., The Chemical and Ionization Conditions in Weak Mg II Absorbers, 2008, Astrophysical Journal, Volume 689, Issue 2, pp. 782-815.  MORE INFO
- Misawa, T., Charlton, J. C., &Narayanan, A., Supersolar Metallicity in Weak Mg II Absorption Systems at z ~ 1.7, 2008, Astrophysical Journal, Volume 679, Issue 1, pp. 220-238.  MORE INFO
- Narayanan, A., Misawa, T., Charlton, J. C., & Kim, T-S., A Survey of Weak Mg II Absorbers at 0.4 < z < 2.4, 2007, Astrophysical Journal, Volume 660, Issue 2, pp. 1093-1105.  MORE INFO
- Narayanan, A., Misawa, T., Charlton, J. C., & Ganguly, R., The Advantage of Increased Resolution in the Study of Quasar Absorption Systems, 2006, Astrophysical Journal, Volume 132, Issue 5, pp. 2099-2113.  MORE INFO
- Narayanan, A., Charlton, J. C., Masiero, J. R., & Lynch, R., A Survey of Analogs to Weak Mg II Absorbers in the Present, 2005, Astrophysical Journal, Volume 632, Issue 1, pp. 92-109.  MORE INFO
STUDENT MENTORING
List of students who have worked with me on short term and long term projects. Some of these were project based learning (pedagogical in nature), and some worked on segments from my own research work.
- 2014-2017:   Sachin P C, Indian Institute of Space Science & Technology, Ph D work
- 2011:   Savithri Ezhikode, School of Pure & Applied Physics, Mahatma Gandhi University Kottayam
- 2013:   Keerthi Sasidharan, Rahna P T, School of Pure & Applied Physics, Mahatma Gandhi University Kottayam
- 2013:   Rahul Poruri, Indian Institute of Technology, Chennai
- 2013:   Sachin P C, Indian Institute of Space Science & Technology (Ph D student)
- 2014:   Unnikrishnan Potty, Maharaja's College, Ernakulam
- 2015:   Sangeetha Sudheer, Revathi P P, Devamatha College, Kuravilangadu
- 2015:   Anusree K G, Pondicherry University
- 2016:   Joel D'Cruz, Indian Institute of Space Science & Technology
- 2016:   Sreerag S J, University College, Thiruvananthapuram
- 2016:   Jayalekshmi Pradeep, Government College for Women, Thiruvananthapuram
- 2017:   Gayathri Prasad, Sreelakshmi M Nair, Nayantara Rose Jose, Nandana Uthaman, Alphonsa College, Palai
- 2016-2017:   Kshitija Pawar, Indian Institute of Space Science & Technology, MS - Astrophysics
- 2017:   Gayathri Prasad, Sreelakshmi Nair, Nayantara Jose, Nandana Uthaman, Alphonsa College, Pala
- 2017:   Gayathri Prasad, Sreelakshmi Nair, Nayantara Jose, Nandana Uthaman, Alphonsa College, Pala
- 2017:   Betty Jose, Honey Pinto, Mercy College, Palakkad
- 2017-2018:   Aditya Manuwal, Indian Institute of Space Science & Technology, MS - Astrophysics
- 2018:   Arun Seshadri, Sree Vasya NSS College, Thrissur
- 2018:   Vishnu Varma, Sree Kerala Varma College, Thrissur
- 2018:   Sreelakshmi Sudarshan, Sreepriya C, NSS College, Ottapalam
- 2018-2019:   Jayadev Pradeep, Indian Institute of Space Science & Technology, MS - Astrophysics
- 2018-ongoing :   Sriram Sankar, FISAT
- 2019-ongoing :   Pratyush Anshul, Indian Institute of Space Science & Technology, MS - Astrophysics
- 2019-ongoing :   Mathin Yadav, Indian Institute of Space Science & Technology, Dual Degree - Astrophysics
- 2019-ongoing :   Purvi Udhwani, Indian Institute of Space Science & Technology, Junior Research Fellow