J/ApJ/950/81 Star-forming regions of NGC4395 with UV & Ha obs. (Nandi+, 2023)
Star formation in the dwarf Seyfert galaxy NGC 4395: evidence for both AGN and
SN feedback?
Nandi P., Stalin C.S., Saikia D.J., Muneer S., Mountrichas G.,
Wylezalek D., Sagar R., Kissler-Patig M.
<Astrophys. J., 950, 81 (2023)>
=2023ApJ...950...81N 2023ApJ...950...81N
ADC_Keywords: Galaxies, Seyfert; Active gal. nuclei; Star Forming Region;
Photometry, ultraviolet; Extinction; Optical; Infrared
Keywords: Active galactic nuclei ; Seyfert galaxies ; Star formation ;
Galaxy photometry ; Radio continuum emission
Abstract:
We present a detailed multiwavelength study of star formation in the
dwarf galaxy NGC 4395, which hosts an active galactic nucleus (AGN).
From our observations with the Ultra-Violet Imaging Telescope, we have
compiled a catalog of 284 star-forming (SF) regions, out of which we
could detect 120 SF regions in Hα observations. Across the
entire galaxy, we found the extinction-corrected star formation rate
(SFR) in the far ultraviolet (UV) to range from 2.0x10-5M☉/yr
to 1.5x10-2M☉/yr with a median of 3.0x10-4M☉/yr, and
the age to lie in the range of ∼1 to 98Myr with a median of 14Myr. In
Hα we found the SFR to range from 7.2x10-6M☉/yr to
2.7x10-2M☉/yr with a median of 1.7x10-4M☉/yr, and the
age to lie between 3 to 6Myr with a median of 5Myr. The stellar ages
derived from Hα show a gradual decline with galactocentric
distance. We found three SF regions close to the center of NGC 4395
with high SFRs both from Hα and UV, which could be attributed to
feedback effects from the AGN. We also found six other SF regions in
one of the spiral arms having higher SFRs. These are very close to
supernova remnants, which could have enhanced the SFR locally. We
obtained a specific SFR (SFR per unit mass) for the whole galaxy of
4.64x10-10yr-1.
Description:
For this work, we used our new observations (UV and Hα) as well
as archival data (radio, IR, and broadband optical).
We observed NGC 4395 in the UV band using the Ultra-Violet Imaging
Telescope (UVIT), one of the payloads on board AstroSat India's first
multiwavelength astronomical observatory launched by the Indian Space
Research Organization (ISRO) in 2015 September. UVIT observes
simultaneously in three channels, namely far-UV (FUV; 1300-1800Å),
near-UV, (NUV; 2000-3000Å), and the visible (VIS; 3200-5500Å)
over a field of view of diameter with spatial resolution better than
1.5" in the UV. NGC 4395 was observed by UVIT on 2018 February 27 in
the photon counting mode with the default frame rate of ∼34 frames
per second.
Optical observations in the narrow Hα and broad R band were
obtained on 2021 December 22, using the Himalayan Faint Object
Spectrograph Camera (HFOSC) instrument mounted on the 2m Himalayan
Chandra Telescope (HCT) situated in the Indian Astronomical
Observatory, Hanle, India. Three exposures each of 600s or a total of
1800s was taken in narrowband Hα and one frame of 300s in the R
band. These observations have a spatial resolution between 1.9" and 2.2".
In addition to the observations acquired in Hα, we also used
archival data in the broadband U, B, V, R, and I filters from the
Nordic Optical Telescope (NOT).
In the IR, we used archival images (from NE) in the J, H, and Ks bands
from the Two Micron All Sky Survey (2MASS; see VII/233), and the W1
(3.4um), W2 (4.6um), and W3 (12um) bands taken from the Wide-field
Infrared Survey Explorer (WISE; see II/311). Also, in the far-IR, we
used data at 24, 70, and 160um from the Multiband Imaging Photometer
for Spitzer (MIPS) instrument on Spitzer.
We used observations from the Very Large Array (VLA) carried out at
1.4GHz in its C configuration. We also have archival data at 1.4GHz
from the VLA in the A and B configurations. However, in the A and B
configuration data, only the central AGN is detected. Therefore, in
this work we used only the data in the C configuration, the processed
image of which was taken from the archives of the VLA. We also used
21cm HI emission line data from the Westerbork Synthesis Radio
Telescope (WSRT).
Objects:
--------------------------------------------------------------
RA (ICRS) DE Designation(s)
--------------------------------------------------------------
12 25 48.86 +33 32 48.7 NGC 4395 = 2MASX J12254892+3332482
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 85 284 Catalogue of star-forming (SF) regions in NGC 4395
table4.dat 93 14 Star formation rate (SFR) in multiple wavelengths
determined for the 14 SF regions identified in
the MIPS 24um image
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See also:
VII/233 : 2MASS All-Sky Extended Source Catalog (XSC) (IPAC/UMass, 2003-2006)
II/311 : WISE All-Sky Data Release (Cutri+ 2012)
J/A+A/391/809 : HII regions in NGC 5457 and NGC 4395 (Cedres+, 2002)
J/ApJ/632/799 : NGC4395 light curves (Peterson+, 2005)
J/AJ/138/1243 : The star formation history of the LMC (Harris+, 2009)
J/ApJ/703/1672 : Far-IR and Hα fluxes in galaxies (Kennicutt+, 2009)
J/ApJ/706/599 : Hα and UV SFR in the local volume (Lee+, 2009)
J/ApJ/744/44 : Hα and UV fluxes in nearby galaxies (Weisz+, 2012)
J/MNRAS/429/189 : SNRs in six nearby galaxies (Leonidaki+, 2013)
J/MNRAS/451/3173 : Circumnuclear star-forming regions (Alvarez-Alvarez+, 2015)
J/AJ/150/43 : Star formation in active and normal galaxies (Tsai+, 2015)
J/ApJ/847/136 : Hβ to N2 line fluxes of nearby galaxies (Brown+, 2017)
J/ApJ/872/16 : Star formation law revisited. I. (de los Reyes+, 2019)
J/ApJ/892/93 : UV-NIR monitoring campaign of NGC 4395 (Cho+, 2020)
J/ApJ/896/10 : NSA low-mass galaxies with PTF obs. (Baldassare+, 2020)
J/ApJ/934/L37 : NGC 4395 FTN/MuSCAT3 photometry obs. (Montano+, 2022)
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.6 deg RAdeg [186.36/186.6] Right Ascension (J2000)
12- 20 F9.6 deg DEdeg [33.47/33.7] Declination (J2000)
22- 26 F5.3 arcsec amaj [0.84/7.9] Semi-major axis, star
forming region
28- 32 F5.3 arcsec bmin [0.58/4.3] Semi-minor axis, star
forming region
34- 40 F7.3 deg PA [0/360] Position angle, star forming
region
42- 47 F6.3 mag magFUV [14/21.3] Extinction corrected
UVIT/F148W magnitude
49- 54 F6.3 mag magNUV [14.2/21.1] Extinction corrected
UVIT/N263M magnitude
56- 61 F6.3 mag AFUV [-1.2/4.97] Extinction, F148W
63- 68 F6.3 mag ANUV [-0.9/3.61] Extinction, N263M
70- 74 F5.3 Msun/yr/kpc2 SSFRFUV [0.005/2.6] Extinction corrected
surface density of star formation rate,
F148W
76- 80 F5.3 Msun/yr/kpc2 SSFRNUV [0.007/1.91] Extinction corrected
surface density of star formation rate,
N263M
82 A1 --- l_ageUV Limit flag on age-UV (1)
83- 85 I3 Myr ageUV [1/100] Age calculated in UV
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Note (1): Ages include upper (<1.) and lower (>100.) Myr limits
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Seq [1/14] Sequential MIPS SFR identifier
4- 13 F10.6 deg RAdeg [186.35/186.52] Right Ascension (J2000)
15- 23 F9.6 deg DEdeg [33.5/33.62] Declination (J2000)
25- 29 F5.2 arcsec amaj [3.97/23.1] Semi-major axis, star
forming region
31- 36 F6.3 arcsec bmin [3.1/17.3] Semi-minor axis, star forming
region
38- 43 F6.2 deg PA [-89.7/88.3] Position angle, star
forming region
45- 49 F5.3 10-3Msun/yr SFRFUV [0.02/4.2] Star formation rate, FUV
51- 55 F5.3 10-3Msun/yr e_SFRFUV [0.001/0.06] Uncertainty in SFR-FUV
57- 61 F5.3 10-3Msun/yr SFRNUV [0.02/4.2] Star formation rate, NUV
63- 67 F5.3 10-3Msun/yr e_SFRNUV [0.001/0.05] Uncertainty in SFR-NUV
69- 74 F6.3 10-3Msun/yr SFRHa [0.006/13.5] Star formation rate, Hα
76- 80 F5.3 10-3Msun/yr e_SFRHa [0.001/0.008] Uncertainty in SFR-Ha
82- 87 F6.3 10-3Msun/yr SFR24um [0.36/10.7] Star formation rate, 24um
89- 93 F5.3 10-3Msun/yr e_SFR24um [0.16/1] Uncertainty in SFR-24um
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 28-Jul-2025