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Science research:
Science research:
Star formation (SF) and physics of the interstellar medium (ISM) play a crucial role in evolution of galaxies. The purpose of my research is to shed more light on the physics of the ISM and evolution of galaxies in the nearby universe.
We achieved this by deriving the effects of internal dust on attenuating galactic emission, constraining uncertainties in measuring the star-formation rate (SFE) prescriptions, and probing the properties of the diffuse ionized gas in the tails of stripped galaxies of galactic groups and clusters.
1) What is affecting measurements of star-formation rates in the Andromeda galaxy?
1) What is affecting measurements of star-formation rates in the Andromeda galaxy?
The attenuation of light from galaxies is caused by internal dust, which is an important ISM component. The light emission from the ionized gas is one of the most important tracers and measuring tools of the star formation rates in nearby galaxies. So, probing the relative distribution of the ionized gas and dust, and their effects on attenuation play a key role in removing uncertainties in measuring the SFRs of nearby galaxies.
I used optical Integral Field Unit (IFU) observations of the outskirts of the Andromeda galaxy (M 31), taking advantage of its proximity, to probe star-forming regions at a spatial resolution of ~10 pc. I derived the (3-dimensional) dust/gas geometry in M 31 by comparing the attenuation of the nebular lines with the dust mass surface densities. We found that the M 31 data follows more the foreground screen model, which differs from the geometry found in a survey of nearby galaxies (KINGFISH survey). My hypothesis for the origin of the difference in the gas/dust distributions between M 31 and these other nearby galaxies is that the vertical distribution of the dust, star-forming regions, and the diffuse ionized gas changes with galactocentric radius and with inclination.
We then used multi-wavelength images of M 31 to calibrate the SFR prescriptions and compare them with established hybrid SFR prescriptions from literature. I found that the hybrid SFR prescriptions are not universal, and that variable relative distribution of HII, DIG and dust alters the SFR prescriptions at different radii, as hypothesised before.
This work is a part of my papers: Tomicic et al. 2017 (ApJ 844 155T) and Tomicic et al. 2019 (ApJ 873, 1).
Figure: Five fields in Andromeda galaxy (M 31) that we observed with IFU and use. Credit: Tomicic et al. 2017, ApJ 844 155T
Figure: Attenuation (y-axis) vs. dust mass surface density (x-axis) with data of the M 31 Fields data (black dots) and nearby galaxies (gray dots). Over-plotted with yellow-black dashed lines are two models for relative dust/gas spatial distribution (screen and mixed models) and lines of my toy model with different fraction of the diffuse ionised gas in front of the dust. Credit: Tomicic et al. 2017, ApJ 844 155T
2) Properties of diffuse gas in the tails of cluster galaxies
2) Properties of diffuse gas in the tails of cluster galaxies
Galaxy clusters are good laboratories of galaxy evolution and offer an opportunity to probe the effects of the environments on the physics of the ISM and the host galaxies. Many galaxies that are infalling to the groups and clusters are being stripped due to the ram-pressure stripping process caused by the inter-cluster medium, which can both temporarily increase star formation and then quench it within the galactic disks. The stripped gas of those galaxies may form new stars in the tails of those stripped galaxies, outside their disks. The GASP collaboration works on probing the stellar and the ISM components of those stripped galaxies.
My work within the GASP collaboration concentrates on deriving the method of measuring the fraction of the diffuse ionized gas across these stripped galaxies. Furthermore, I investigate various properties of that gas across different phases of galaxy evolution and stripping process.
We observe that these striped tails are highly diffuse, and show ionization coming from processes other than star-formation. We hypothesize that the DIG in the tails is at least partly ionized by a process other than star-formation, probably by mixing, shocks, and accretion of inter-cluster and interstellar medium gas.
This work is a part of my papers: Tomicic et al. 2021 (ApJ, 907, 22T) and Tomicic et al. 2021b (ApJ in press).
Figure: Galaxy maps of a control galaxy (top panels) and gas-stripped galaxies (middle and bottom panels). From left to right: R-band and observed Hα (ionized gas) image, DIG emission fraction (Cdig), ionization parameter log(q), and Δlog[OI]/Hα (red for star-forming and blue for LIER source of ionisation).
3) Large (3 dex) variation in SFE in interacting galaxy NGC 2276
3) Large (3 dex) variation in SFE in interacting galaxy NGC 2276
Recent simulations of interacting galaxies indicated that the star-formation efficiency (SFE=1/depletion time) may be affected by the turbulence generated by the tidal forces. To test this hypothesis, we estimated SFE of the nearby star-forming galaxy NGC 2276, a pre-coalescence interacting galaxy.
I measured the SFR of NGC 2276 at sub-galactic scales (~0.5 kpc) from the optical IFU observations (PPaK/PMAS from Calar Alto), and combined it with CO(1-0) data, observed by using the IRAM facilities. I found 3 orders of magnitude of range in SFE of the bulk of molecular gas. Also, I found a gradual variation from one side of the galaxy, toward another side.
This unusually large variation in the SFE at sub-kpc scales is larger than the variation found in the HERACLES survey of galaxies, despite NGC 2276's mean galactic SFE value being within the HERACLES scatter. We speculate that this large variation in SFE is caused by tidal forces exerted from the neighboring galaxy NGC 2300 and ram pressure affecting the ISM in NGC 2276.
This work is a part of my paper, Tomicic et al. 2018, ApJL 869 L38.
Figure: The SFE map (inverse of the depletion time) of the bulk molecular gas of NGC 2276, a pre-coalescence interacting galaxy. The direction toward the neighbouring elliptical galaxy NGC 2300 is marked in the bottom left corner. Credit: Tomicic et al. 2018, ApJL 869 L38.
Figure: Kennicutt-Schmidt diagram for the pre-coalescence interacting galaxy NGC 2276 (~0.5 kpc scale data: orange crosses; mean galactic value: thick green cross); the HERACLES survey of galaxies (contours; Leroy et al. 2013); mid-stage merger VV 114; luminous merger remnant NGC 1614; and Antennae merger galaxy. Credit: Tomicic et al. 2018, ApJL 869 L38.
Figure: Example of a simulated protocluster and background galaxies within the specific redshift bin. We mark the "measured" effective radius of observed system.
4) Contamination and completeness of protoclusters of galaxies at high redshift in COSMOS field
4) Contamination and completeness of protoclusters of galaxies at high redshift in COSMOS field
This work is a part of my Master thesis, and a part of Smolčić, Miettinen, Tomičić et al. 2016, A&A, 597, A4.
The galaxy clusters are large virialized collections of galaxies, formed from galaxy protoclusters in early universe (redshifts z=2-5). Due to uncertainty in determining the proper photometric redshifts of galaxies in the protoclusters of the COSMOS survey, I derived a Monte Carlo simulation to determine the contamination and completeness of probed protoclusters.
The results show that completeness (~85%) of the proto-clusters does not change compared to the redshift, while the contamination expectedly increases with distance from the center of protoclusters. The calculated effective radii of our simulated protoclusters agree within a factor of 2 with the initial effective radii of protoclusters. This indicates that 60%-70% of galaxies of the protoclusters are within the "measured" effective radius, regardless of redshift.
Projects and collaborations:
Projects and collaborations:
1) Current project
1) Current project
GASP:
"GAs Stripping Phenomena in galaxies with MUSE"; ESO (MUSE+ALMA+IRAM) large program of interacting and ram pressured "jellyfish" galaxies (PI B. Poggianti). The aim of this program is to clarify how, where and why the gas removal occurs, measure its timescale and efficiency as a function of galaxy mass and environment, and quantify the amount of star formation involved in this process.
Within the GASP project, I am currently working on analysis of the diffuse ionized gas, stellar cluster age determination, and observation of dust in the tails of the jellyfish galaxies.
Image: Example of jellyfish galaxies. White is stellar continuum, and red is ionised gas emission indicating star-forming regions (credit: ESO/GASP collaboration).
2) Participation in projects
2) Participation in projects
COSMOS - "The Cosmic Evolution Survey"; Survey designed to probe the formation and evolution of galaxies as a function of both cosmic time (redshift) and the local galaxy environment.
EMPIRE - "EMIR Multiline Probe of the ISM Regulating Galaxy Evolution"; Large program (PI F. Bigiel) at the IRAM 30m mm-wave telescope which will provide for the first time extended maps of a suite of dense gas tracers (e.g., HCN, HCO+, HNC) for a sample of nearby, star-forming, disk galaxies.
3) Collaborations with Projects
3) Collaborations with Projects
PHANGS - "Physics at High Angular resolution in Nearby GalaxieS"; Large program observations (MUSE+ALMA+HST+VLA+...) of nearby galaxies to understand how physics at or near the “molecular cloud” scale are affected by galaxy-scale conditions. The aim is to understand the interplay of the small-scale physics of gas and star formation with galactic structure and galaxy evolution.
HASHTAG - "HARP and SCUBA-2 High Resolution Terahertz Andromeda Galaxy Survey"; Large Program on the JCMT to observe the entirety of Andromeda with SCUBA-2 at 450 and 850μm, and to observe selected regions in CO(=3-2) with HARP.
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