Projects

The Isaac Newton Telescope monitoring survey of Local Group dwarf galaxies

IC10 dwarf, INT Project

Presenting a complete suite of galactic environments, dwarf galaxies are the most abundant type of galaxies in the Universe. Due to their proximity, variety, and a wide range of metallicity, the Local Group dwarf galaxies offer a unique opportunity to study the connection between stellar populations and galaxy evolution. In this regard, an optical monitoring survey in nearby dwarf galaxies was carried out with the 2.5 m Isaac Newton Telescope. Fifty-five dwarf galaxies and four isolated globular clusters in the Local Group were observed with the Wide Field Camera. The main aims of this survey are to identify the most evolved asymptotic giant branch (AGB) stars and red supergiants (RSGs) at the end-point of their evolution based on their pulsational instability, use their distribution over luminosity to reconstruct the star formation history, quantify the dust production and mass loss from modeling the multiwavelength spectral energy distributions (SEDs), and relate this to luminosity and radius variations. The variety among nearby galaxies offers a superb opportunity to study the pulsational behaviour of evolved stars as a function of metallicity and stellar mass (Saremi et al. 2020).

The main priority of our survey was the observation of the majority of Andromeda satellites because these are all accessible to a Northern hemisphere survey and provide an excellent sample due to homogeneity in distances, completeness, accuracy, and foreground contamination and extinction. In order to find out whether the Andromeda system could be considered as a universal template for galaxy evolution or it is just a particular case, the Milky Way satellites were also observed for comparison. Also, we included four distant GCs: Sextans C, Segue III, NGC 2419 and Palomar 4, to investigate the possibility of them being stripped nucleated dwarf galaxies. Also, with the observation of massive spiral galaxy, NGC 6946, we are looking the most luminous LPVs in it to identify dusty supernova (SN) progenitors for follow-up with JWST.

Star Formation History and Dust Production in M33

Triangulum (M33), VLT Survey Telescope

M33 is the nearest spiral galaxy besides the Andromeda galaxy, and seen under a more favorable angle. This makes M33 ideal to study the structure and evolution of a spiral galaxy. We will thus learn how our own galaxy the Milky Way formed and evolved, which is difficult to do directly due to our position within its dusty disc. We will confront our findings with theories of galaxy formation and evolution within cosmological models such as Lambda Cold Dark Matter.

In the final stage of stellar evolution, low-medium mass (0.8-8 𝑀⊙) stars enter the AGB phase and more massive stars (M > 8 𝑀⊙) enter the RSG phase. These two phases of evolution trace stellar populations over a range in age from 10 Myr to 10 Gyr, and hence the evolution of their host galaxies over essential all cosmological time. Radial pulsation of the atmosphere layers in AGB stars and RSGs yield long-period variability of order 150-1500 days in the photometric light curves. Most evolved AGB stars pulsate in fundamental mode, while less evolved AGB stars pulsate in an overtone; as a result, the amplitude of variability expressed in magnitude of AGB stars are larger than that of RSGs and less evolved AGB stars. These LPVs are powerful tools to study the star formation history of galaxies, and to this aim various variability surveys have been conducted of M33 over recent years (e.g., Hartman et al. 2006; McQuinn et al. 2007).

The project exploits our large observational campaign between 2003 -2008, over 100 hrs on the UK InfraRed Telescope. In first instance, only the central square kiloparsec were monitored and analysed, with the UST camera. The variable stars catalogue and SFH were presented in Javadi et al. (2011a, b, c); we found a main formation epoch of redshift 1, but with fluctuations up to the present day. We have finished stage 3, quantifying the mass return and comparing it with the mass consumption by star formation (Fig. 1; Javadi et al. 2013). As the new wide-field camera (WFCAM) became available the campaign was expanded to cover two orders of magnitude larger area, comprising the disc of M33 and its spiral arms. We are now ready to enter this new phase of analysis, the long period variables are identified (Javadi et al. 2015); we will apply the tools developed and validated previously, also to other Local Group galaxies (e.g., Rezaeikh et al. 2014; Hamedani Golshan et al. 2017).

The main objectives of the project are: to construct the mass function of LPVs and derive from this the star formation history in M33; to correlate spatial distributions of the LPVs of different mass with galactic structures (spheroid, disc and spiral arm components); to measure the rate at which dust is produced and fed into the ISM; to establish correlations between the dust production rate, luminosity, and amplitude of the LPVs; and to compare the in situ dust replenishment with the amount of pre-existing dust.

We will thus show how SFH varies across M33, e.g. whether star formation has propagated inwards or outwards through the disc (Javadi et al. 2017); we will measure the lag between stars of different ages and the spiral arms in which they formed; and we will show where mass is returned, how this compares to the gas in spiral arms and inter-arm regions, and from this estimate gas recycle times and gas depletion in star formation (Yuan et al. 2018).

Left: Spitzer composite image of IRAC bands 1, 2 and 4 at respectively 3.6 𝜇𝑚 (blue), 4.5 𝜇𝑚 (green) and 8 𝜇𝑚 (red); Right: map of mass return-rate surface density over the central region of M33

Star Formation History and Dust Production in some of nearby galaxies; LMC & SMC, NGC 147 & NGC 185, IC 1613, NGC 5128, NGC 6822, M 31

NGC 6822 MPG/ESO Telescope

LPV stars of some galaxies in and out of the Local Group have been identified by other projects. Given that there were some limitations in our observation time with INT, we have not observed such galaxies again, and, therefore, we use those already-identified variable stars to get the evolution of their host galax-ies using our method. This will also extend our sample, which results in a better understanding of the formation and evolution of galaxies in our neighborhood. Here, we briefly introduce these works and their results:

LMC & SMC: For the nearby, relatively massive and interacting gas-rich dwarf galaxies, the Magellan-ic Clouds, we found that the bulk of the stars formed∼10 Gyr ago for the LMC, while the strongest epi-sode of star formation in the SMC occurred a few Gyr later. A peak in star formation around 0.7 Gyr ago in both Clouds is likely linked to their recent interaction (Rezaeikh et al. 2014).

NGC 147 & NGC 185: The Andromeda satellite pair NGC147/185 show different histories; the main epoch of star formation for NGC 185 occurred 8.3 Gyr ago, followed by a much lower, but relatively constant star formation rate (SFR). In the case of NGC 147, the SFR peaked only 6.9 Gyr ago, staying intense until∼3 Gyr ago (Hamedani Golshan et al. 2017).

IC 1613: We present an analysis of the star formation history (SFH) of a field of ∼200 arcmin2 in the central part of the IC1613. The absence of a dominant epoch of star formation over the past 5 Gyr sug-gests that IC 1613 has evolved in isolation for that long. We confirm the radial age gradient, with star formation currently concentrated in the central regions of IC 1613, and the failure of recent star formation to have created the main Hi supershell (Hashemi et al. 2019).

NGC 5128: NGC 5128 is the nearest easily observable giant elliptical galaxy at the distance of 3.8 Mpc, out of the Local Group. Using identified LPVs in two small fields in the halo and in northern and southern part of the galaxy, for the first time, we will present the deep SFH of those fields, as a tracer to the evolution of the galaxy.

NGC 6822: NGC6822, an isolated dwarf irregular galaxy (dIrr), due to close distance, apparent isola-tion, and easy observation, has been always selected as a desired candidate for studying star formation and galactic evolution, without the strong gravitational influences of other systems. To calculate the SFH in the bar of the galaxy, we use more than 600 LPV stars from different catalogues that are included the main part of the LPVs and RSG stars.