INT Proposal. Santos; Loukotová. Measurement of the Hα flux in the nearby early-type galaxy NGC Abstract

Transcription

1 Santos; Loukotová INT Proposal Measurement of the Hα flux in the nearby early-type galaxy NGC 4203 Abstract The evolution of galaxies is one of the most rich fields of research on current Astronomy, and it is of particular interest for us to know the star formation rates of nearby (z ~ 0) galaxies in different phases. Previous investigations found structures that indicate star formation activities in the outskirts of the early-type galaxy NGC 4203, but there is no sufficient data or information about this region on the Hα narrow band. This study aims to observe the Hα luminosity on the disk of this galaxy, and with that, place stronger constraints in its star formation rate. Time requested (nights) Dark Grey Bright Minimum useful allocation (nights) Dark Grey Bright 0 0 1

2 Applicants Name Affiliation Country Potential observer Mustafa Yildiz Leonardo Santos Rijksuniversiteit Groningen (Kapteyn Astronomical Institute) Universidade Federal de Itajubá (Instituto de Física e Química) mkyildiz@astro.rug.nl The Netherlands laugusto@unifei.edu.br Brazil Yes Klára Loukotová Masaryk University loukotovak@seznam.cz Czech Republic Yes Summary of observations Field RA Dec Epoch Magnitude Colour Exposure (sec.) NGC :15: :11:50.08 J (estim.) R 800 Conduct project in visitor mode Overall scheduling requirements Any night in the week at the Observatory will suffice, for NGC 4203 is easily observable during April. Since the object crosses the meridian at 1:40 AM local time, we request a time allocation of 2 hours around this time (necessary to conduct the observation of the galaxy at Hα, the continuum and standard stars). Overall scheduling preferences From our estimations of the Hα luminosity of the galaxy disk from the star formation rate, there is no need to allocate a grey sky. Summary of backup programme for poor Observing conditions In case of poor conditions of seeing and/or transparency conditions, we intend to simply measure the magnitude of the galaxy disk (if visible), which would help constrain the star formation rate. Experience of intended observers who have not previously used this telescope L. Santos had a brief experience (5 nights) in spectroscopic observations of planetary nebulae using the 1.6 m telescope at Pico dos Dias Observatory, located in Brazil. K. Loukotová had an experience of 3 nights doing spectroscopic observations at Ondřejov 2m telescope, located in Czech Republic and photometric observations with the 0.62 m telescope on MonteBoo Observatory, Masaryk University, Czech Republic. Instrumental setup Focal station Instrument Detector(s) Gratings/Filters Prime Focus INT WFC WFCH6568, WFCHARR Students involved Student Level Applicant Supervisor Applicant Expected completion date Data required Leonardo Santos Bachelor Yes Mustafa Yildiz Yes 2015/07 Yes Klára Loukotová Master Yes Mustafa Yildiz Yes 2015/06 Yes

3 Linked proposals submitted to this TAC: No Linked proposals submitted to other TACs: No Relevant previous allocations: No Related publications: The ATLAS 3D project - I. A volume-limited sample of 260 nearby early-type galaxies: science goals and selection criteria Capellari, M. et al., 2011 Published on the Monthly Notices of the Royal Astronomical Society, Volume 413, Issue 2, pp Discussion of data analysis plan: The main idea of this observation is to provide an opportunity for the students Leonardo Santos and Klára Loukotová to have a hands-on experience with real observations, data reduction and obtaining information. For that, the data analysis plan is to use some of the well-established routines on IRAF to reduce the data and to calculate the fluxes in the Hα on the galaxy disk, which would place stronger constraints at the star formation rate. This data are intended to support the investigations done in the Atlas 3D survey. No additional remarks

4 Scientific justification As judged by the usual classification criteria, NGC 4203 is a fairly typical S0 (lenticular) galaxy. The position of S0 galaxies in the morphological classification between ellipticals and spirals makes them particularly attractive regarding our knowledge of the formation and evolution of galaxies. NGC 4203 is even more attractive since unlike most S0 s, it is embedded in an HI disk with the diameter of roughly 20 kpc. The role o this far-flung HI in the evolution of the galaxy remains uncertain. In order to explore this topic, star formation rate (SFR) would be a good indicator of how the neutral gas affects its host galaxy. An estimation of SFR in the disk of the galaxy NGC 4203 was performed using far-ultraviolet photometry from GALEX telescope, by using the Schmidt law or star formation law which resulted in ~ 10-3 M /yr in the outer region of the galaxy. We would like to compare this value with the one obtained from Hα measurements using the empirical relation derived by Kennicutt And also to explore the correlation between SFR and HI column density. Another interesting point to this galaxy is the presence of a supposed smaller companion, which can be seen as a blue fuzzy patch to the east direction, in figure 2. Investigators have conjectured that the arm-like structure observed in radio frequencies (figure 1) is caused by gravitational interactions with that satellite galaxy. The observations that we intend to perform may help to understand the nature of these features. Existing imaging data: NGC 4203 are imaged by the Atlas 3D, SDSS and 2MASS surveys, but data from Hα narrow band exists only for the central region of the galaxy, and not for the disk. Figure 1. Star formation rates for the galaxy NGC 4203 using FUV data

5 Figure 2. Total HI contours on top of DSS image. The value on the lower right is the column density of HI (Serra et al. 2011) Technical justification When observed on surveys, NGC 4203 appears as an 11th magnitude elliptical galaxy approximately 2' across. But recent observations in radio show a disk-like structure as wide as ~5' across (see figure 2). There are no measurements of the Hα narrow line on the disk of NGC 4203, only for the galaxy center (e.g. Shields et al. 2000), but using the previous estimation of the SFR, we can calculate the expected luminosity of the galaxy disk in the Hα narrow band, using the empirical relation: SFR= L(H α) This means that, if we can measure (or even detect, for that matter) the flux of the disk in the Hα narrow band, it will help clarify the understanding of the nature of the structure, besides placing stronger constraints in the star formation rate in that region. It is also important to note that the distance to the galaxy has been measured previously, the values being around 17.2 Mpc (e.g. Theureau et al. 2007). However, these discrepancies do not result in significant differences in the magnitude of the galaxy disk, which makes it easier to estimate the necessary exposure time (table 1). Table 1. The approximate exposure times to achieve 5 S/N ratio using the requested instrumental setup Apparent Magnitude Grey sky Bright sky s 150 s s 800 s s 4000 s Using the previous SFR/L(Hα) relation, we obtain an apparent magnitude of ~20 for a 17.2 Mpc distant galaxy. Considering that this is far from being an accurate estimation, we assert that it is safer to observe using a time slot equivalent to a 21 st magnitude object. Since there's no stronger constraints at the SFR at this point (not even uncertainties), it is difficult to make better estimations. Our plan is to perform an observation in Hα narrow band with 800 s of exposure time (assuming bright sky conditions). The same exposure time must then be used to obtain the continuum in the R-band. Besides those, it is also needed to include time to observe standard stars, pointing the telescope, cycle time of the CCD, and to get acquainted with the instruments. These are the reasons for the request of a 2-hour long time allocation.

6 Another crucial point of this observation is the presence of a bright (11.5 magnitude in the R-band) F6-type star (HD ) in the field of view (situated between 2 and 3 away from the center of NGC 4203). From our calculations, it can saturate the CCD in this particular instrumental set in about 60 seconds in Hα narrow band, which means that the observation run would have to be broken down into s. Data for the continuum is also affected, because this star saturates the CCD in R-band in roughly 3.5 seconds, which means that we would need to take s exposures. However, this is not going to be possible due to the cycle time of the CCD, but these intervals could be extended if we consider that the FWHM for INT is of the order of 1.0~2.0. It means that even if the star saturates, it would not heavily affect the observation of the galaxy disk for a sufficiently low exposure interval. The problem of saturation of the CCD can be circumvented by shifting the bright star to one of the gaps of the detector (which measure approx. 1 across), and it means that it would not be necessary to break the exposure time into intervals (but it would cause bordering effects). Observation details Field RA Dec Epoch Magnitude Colour Exposure (sec.) NGC :15: :11:50.08 J (estim.) R 800 Lunar Phase Bright Required Scheduling constraints April, 2 hours Preferred Scheduling constraints April 19 th or 20 th, 1 3 AM References Kennicutt R. C., Jr., 1998, ARA&A, 36, 189 Serra P., Oosterloo T., Morganti R., et al. 2012, MNRAS, 422, 1835 Shields, J. C., Rix, H.-W., McIntosh, D. H., et al. 2000, ApJ, 534, L27 Theureau G., Hanski M. O., Coudreau N., Hallet N., Martin J.-M., 2007, A&A, 465, 71