Sasmirala – Individual Information for NGC 4457

Description

NGC 4457 is a low-inclination spiral galaxy in the Virgo cluster at a distance of D = 17.4 ± 3.5 Mpc [tully_nearby_1988], hosting a LINER nucleus [ho_search_1997-1]. The detection of a hard X-ray point source supports the presence of an AGN, while additional diffuse soft emission indicates an AGN/starburst composite nature [satyapal_link_2005, gonzalez-martin_x-ray_2006, flohic_central_2006]. A compact radio source at 6 cm wavelength embedded within a halo with an extent of ~ 10arcsec ~ 840 pc was detected in the nucleus of NGC 4457 (PA~ 177; [van_der_hulst_structure_1981]) but remained undetected at 2 cm [nagar_radio_2002]. We conservatively treat NGC 4457 as an uncertain AGN. The first ground-based MIR observations of NGC 4457 were performed by [scoville_10_1983]. The Spitzer/IRAC and MIPS images reveal an extended nucleus embedded within a prominent spiral pattern. The Spitzer/IRS staring-mode spectrum is dominated by strong PAH emission features with weak silicate 10 μm absorption and a flat spectral slope in νFν-space. Thus, the arcsecond-scale MIR SED is star-formation dominated. Note that [dudik_spitzer_2009] and [pereira-santaella_mid-infrared_2010] report the absence of any significant AGN-indicative [Ne V] emission line in the IRS spectrum. The nuclear region of NGC 4457 was observed with T-ReCS in the Si2 filter during two nights in 2008 [mason_nuclear_2012]. In both images, an ~ 1arcsec ~ 84 pc extended nucleus is weakly detected . Our manually-scaled nuclear PSF photometry is consistent with the PSF-flux reported in [mason_nuclear_2012] and ~ 90% lower than the Spitzer spectrophotometry. Therefore, we conclude that the central ~ 300 pc are completely dominated by star formation emission in the MIR. The subarcsecond data indicates the presence of a nuclear starburst with a possible weak AGN contribution, for which the nuclear flux should be considered an upper limit.

Images

Optical image (DSS, red filter). Displayed are the central 4 arcmin with North being up and East to the left. The colour scaling is linear with white corresponding to the median background (BG) and black to the 0.01% pixels with the highest intensity.

Spitzer MIR images. Displayed are the inner 40 arcsec with North being up and East to the left. The colour scaling is logarithmic with white corresponding to median BG and black to the 0.1% pixels with the highest intensity. The label in the bottom left states instrument and central wavelength of the filter in micron (I: IRAC, M: MIPS).

Subarcsecond-resolution MIR images sorted by increasing filter central wavelength. Displayed are the inner 4 arcsec with North being up and East to the left. The colour scaling is logarithmic with white corresponding to median BG and black to the 75% of the highest intensity of all images in units of sig_bg. The inset image (where present; either bottom or top right) shows the central arcsecond of the PSF from the calibrator star, scaled to match the science target. The labels in the bottom left state instrument and filter names (C: COMICS, M: Michelle, T: T-ReCS, V: VISIR).

SEDs

MIR SED. The description of the symbols in all the SED plots (where present) is the following: Grey crosses and solid lines mark the Spitzer/IRAC, MIPS and IRS data. The colour coding of the other symbols is as follows: green for COMICS, magenta for Michelle, blue for T-ReCS and red for VISIR data. Darker-coloured solid lines mark spectra of the corresponding instrument. The black filled circles mark the nuclear 12 and 18 micron continuum emission estimate from the data (where present). The ticks on the top axis mark positions of common MIR emission lines, while the light grey horizontal bars mark wavelength ranges affected by the silicate 10 and 18 micron features.

Photometry details and reduced FITS files

ObjectRA
[deg]
Dec
[deg]
FilterImageInfoλ_c
[um]
HWHM
[um]
InstrPix. size
[arcsec/pix]
T_exp
[s]
ModeChop Throw
[arcsec]
Chop Angle
[deg]
Rot
[deg]
Prog IdCal. StarCal. DateDate Obs.Factor
[mJy/ct]
Err. Factor
[mJy/ct]
Cal. Flux
[mJy]
Upper Lim. Gauss?F_Gauss
[mJy]
E(F_Gauss)
[mJy]
Upper Lim. PSF?F_PSF
[mJy]
E(F_PSF)
[mJy]
Cal. Maj.
[arcsec]
Cal. Min.
[arcsec]
Cal. PA.
[deg]
Maj. Ax
[arcsec]
Min. Ax
[arcsec]
Pos. Ang.
[deg]
NGC 4457187.2458333.570556Si2NGC4457_Si2_2008-02-20T08-43.fits[Details]8.740.39TRECS0.09927.0PARA15.0-30.00.0GS-2007B-Q-203HD1168702008-02-20T09:35:59Z2008-02-20T08:42:43Z0.01030.0001512286.0False20.40.8False4.80.70.490.4155.01.01.0170.0
NGC 4457187.2458333.570556Si2NGC4457_Si2_2008-03-27T07-07.fits[Details]8.740.39TRECS0.09927.0PARA15.0-30.00.0GS-2007B-Q-203HD1073282008-03-27T07:11:59Z2008-03-27T07:07:40Z0.010660.000157236.0False15.91.4False4.91.40.40.3363.01.00.7837.0