Infrared Survey Facility Research Articles

An FUV and optical study of star formation in closely interacting galaxies: star-forming rings, tidal arms, and nuclear outflows

ABSTRACT We present a study of the morphology of star formation and the associated nuclear activity in a sample of eight closely interacting southern galaxies, which are in different stages of interaction, starting with nearly merged nuclei that have one prominent bulge to more widely spaced interacting galaxies. We have used far-ultraviolet (FUV) observations from the Ultraviolet Imaging Telescope (UVIT), near-Infrared observations from the Infrared Survey Facility (IRSF) telescope, and archival optical data from the Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) integral field spectrograph. Analysing resolved stellar populations across the disc of the interacting galaxies can provide unique insights into how interactions affect galaxy properties, such as morphology, star formation rates, and chemical composition. We take advantage of the unprecedented capabilities of MUSE and UVIT to carry out a highly detailed spatially and spectrally resolved study of star formation rate, star formation histories, metallicity, and active galactic nucleus activity in the sample of eight interacting galaxies that are in different stages of interaction. Most of our sample galaxies are gas-rich and show evidence of recent, massive star formation in tidal tails, rings, and spiral arms. This is evident from their FUV and Hα emissions, which trace young, massive star-forming regions. We compared the star formation rate in the barred and unbarred galaxies in our sample and found that the barred galaxies do not show significant enhancement in star formation rate or large-scale difference in star formation morphology compared to unbarred galaxies. IC5250 and NGC7733N show extended nuclear outflows of sizes ∼5 and 8 kpc, respectively.

Galaxy clusters in the Vela Supercluster – I. Deep NIR catalogues

ABSTRACT We present six deep Near-InfraRed (JHKs) photometric catalogues of galaxies identified in six cluster candidates (VC02, VC04, VC05, VC08, VC10, and VC11) within the Vela Supercluster (VSCL) as part of our efforts to learn more about this large supercluster, which extends across the zone of avoidance (ℓ = 272.°5 ± 20°, b = ±10°, at cz ∼ 18 000 km s−1). The observations were conducted with the InfraRed Survey Facility (IRSF), a 1.4-m telescope situated at the South African Astronomical Observatory (SAAO) in Sutherland. The images in each cluster cover $\sim 80{{\ \rm per\ cent}}$ of their respective Abell radii. We identified a total number of 1715 galaxies distributed over the six cluster candidates, of which only $\sim 15{{\ \rm per\ cent}}$ were previously known. We study the structures and richnesses of the six clusters out to the cluster-centric completeness radius of rc < 1.5 Mpc and magnitude completeness limit of $K_s^o\lt 15{_{.}^{\rm m}}5$, using their iso-density contour maps and radial density profiles. The analysis shows VC04 to be the richest of the six. It is a massive cluster comparable to the Coma and Norma clusters, although its velocity dispersion, σv = 455 km s−1, seems rather low for a rich cluster. VC02 and VC05 are found to be relatively rich clusters while VC08 is rather poor. Also, VC05 has the highest central number density among the six. VC11 is an intermediate cluster that contains two major subclusters while VC10 has a filament-like structure and is likely not to be a cluster after all.

Hidden in plain sight: UVIT and MUSE discovery of a large, diffuse star-forming galaxy

We report the discovery of a nearby large, diffuse galaxy that shows star formation using Ultra Violet Imaging Telescope (UVIT) far-UV observations and archival optical data from Multi-Unit Spectroscopic Explorer (MUSE), Dark Energy Camera Legacy Survey, and InfraRed Survey Facility near-infrared observations. The galaxy was not detected earlier due to its superposition with the background galaxy NGC 6902A. They were together mistakenly classified as an interacting system. NGC 6902A is at a redshift of 0.05554, but MUSE observations indicate that the interacting tail is a separate star-forming foreground galaxy at a redshift of 0.00980. We refer to the new galaxy as UVIT J202258.73–441623.8 (UVIT J2022). The near-infrared observations show that UVIT J2022 has a stellar mass of 8.7 × 108 M⊙. Its inner disk (R < 4 kpc) shows UV and Hαemission from ongoing massive star formation. The rest of the disk is extremely low in luminosity, has a low stellar surface density, and extends out to a radius ofR ∼ 9 kpc. The velocity and metallicity distribution maps and the star formation history indicate that UVIT J2022 has undergone three bursts of star formation. The latest episode is ongoing, which is supported by the presence of widespread Hαand UV emission in its inner disk. The galaxy also shows patchy spiral arms in the far UV, and there is a metallicity enhancement along a bar-like feature. UVIT J2022 is thus a unique example of triggered star formation in a diffuse galaxy resulting in the growth of its inner stellar disk. Our study raises the intriguing possibilities that (i) there could be similar diffuse galaxies that have been mistakenly interpreted as interacting galaxies due to their superposition, and (ii) UV or Hαemission could be a way to detect such diffuse galaxies in our local universe.

The Araucaria Project. Distances to Nine Galaxies Based on a Statistical Analysis of their Carbon Stars (JAGB Method)

Abstract Our work presents an independent calibration of the J-region Asymptotic Giant Branch (JAGB) method using Infrared Survey Facility photometric data and a custom luminosity function profile to determine JAGB mean magnitudes for nine galaxies. We determine a mean absolute magnitude of carbon stars of M LMC = −6.212 ± 0.010 (stat.) ±0.030 (syst.) mag. We then use near-infrared photometry of a number of nearby galaxies, originally obtained by our group to determine their distances from Cepheids using the Leavitt law, in order to independently determine their distances with the JAGB method. We compare the JAGB distances obtained in this work with the Cepheid distances resulting from the same photometry and find very good agreement between the results from the two methods. The mean difference is 0.01 mag with an rms scatter of 0.06 mag after taking into account seven out of the eight analyzed galaxies that had their distances determined using Cepheids. The very accurate distance to the Small Magellanic Cloud based on detached eclipsing binaries is also in very good agreement with the distance obtained from carbon stars.

Three-dimensional dust geometry of the LMC H i ridge region as revealed by the IRSF/SIRIUS survey

Abstract We present a new method to evaluate the dust extinction (AV) along the line of sight using the InfraRed Survey Facility (IRSF) near-infrared (NIR) data of the Large Magellanic Cloud (LMC) H i ridge region. In our method, we estimate an AV value for each star from the NIR color excess and sort them from bluer to redder in each line of sight. Using the percentile values of the sorted AV, we construct a new three-dimensional AV map. We compare the resultant AV map with the total hydrogen column density N(H) traced by velocity-resolved H i and CO observations. In the LMC H i ridge region, Fukui et al. (2017, PASJ, 69, L5) found two velocity components and an intermediate velocity one bridging them. Comparing our three-dimensional AV maps with N(H) maps at the different velocities, we find that the dust geometry is consistent with the scenario of ongoing gas collision between the two velocities as suggested in the previous study. In addition, we find a difference by a factor of 2 in AV/N(H) between the two velocity components, which suggests that inflow gas from the Small Magellanic Clouds (SMC) is mixed in this region. Overall, our results support triggered star formation in 30 Doradus due to the large-scale gas collision caused by tidal interaction between the LMC and the SMC.

The Distance and Peculiar Velocity of the Norma Cluster (ACO3627) Using the Near-infrared J- and K s -band Fundamental Plane Relations

Abstract We report distance measurements for the Norma cluster based on the near-infrared J- and K s -band fundamental plane (FP) relations. Our simultaneous J- and K s -band photometry analyses were performed using 31 early-type galaxies in the nearby Norma cluster obtained using the 1.4 m InfraRed Survey Facility (IRSF) at the South African Astronomical Observatory. Our final K s -band FP sample consists of 41 early-type galaxies from the Norma cluster observed using the IRSF and the New Technology Telescope (NTT) at the European Southern Observatory. This is the largest cluster sample used for peculiar velocity studies in the Great Attractor region to date. From the K s -band FP, we find a distance to the Norma cluster of 4915 ± 121 km s−1. The implied peculiar velocity for Norma is 44 ± 151 km s−1, which further supports a small peculiar velocity for the Norma cluster.

Extinction and dust/gas ratio in the H i ridge region of the LMC based on the IRSF/SIRIUS near-infrared survey

ABSTRACT We present a dust extinction AV map of the Large Magellanic Cloud (LMC) in the H i ridge region using the InfraRed Survey Facility (IRSF) near-infrared (IR) data, and compare the AV map with the total hydrogen column density N(H) maps derived from the CO and H i observations. In the LMC H i ridge region, the two-velocity H i components (plus an intermediate velocity component) are identified, and the young massive star cluster is possibly formed by collision between them. In addition, one of the components is suggested to be an inflow gas from the Small Magellanic Cloud (SMC) which is expected to have even lower metallicity gas (Fukui et al. 2017, PASJ, 69, L5). To evaluate dust/gas ratios in the H i ridge region in detail, we derive the AV map from the near-IR color excess of the IRSF data updated with the latest calibration, and fit the resultant AV map with a combination of the N(H) maps of the different velocity components to decompose it successfully into the three components. As a result, we find difference by a factor of 2 in AV/N(H) between the components. In additon, the CO-to-H2 conversion factor also indicates difference between the components, implying a difference in the metallicity. Our results are likely to support the scenario that the gas in the LMC H i ridge region is contaminated with an inflow gas from the SMC with a geometry consistent with the on-going collision between the two-velocity components.

Interstellar extinction law toward the Galactic center. IV. J, H, and Ks bands from VVV red clump stars

Abstract We have determined the wavelength dependence of the extinction in the near-infrared bands (J, H, Ks) toward the Galactic center from the VVV (VISTA Variables in the Vía Láctea) aperture photometry of the stars in the region |l| ≲ 2${^{\circ}_{.}}$0 and 0${^{\circ}_{.}}$5 ≲ |b| ≲ 1${^{\circ}_{.}}$0; this region consists of 12 VVV tiles. We have found significant systematic discrepancy up to ∼0.1 mag between the stellar magnitudes of the same stars in overlapping VVV tiles. However, by carefully using the positions of red clump stars in color–magnitude diagrams as a tracer of the extinction and reddening, we are able to determine the average of the ratios of total to selective extinction to be $A(K_{\mathrm{s}}) / E(H-K_{\mathrm{s}}) = 1.44\, \pm \, 0.04$, $A(K_{\mathrm{s}}) / E(J-K_{\mathrm{s}}) = 0.423\, \pm \, 0.024$, $A(H) / E(J-H) = 1.25\, \pm \, 0.04$; from these ratios, a steep power law A(λ) ∝ λ−α whose index α is ∼2.0–2.3 in the J, H, Ks wavelength range is estimated. This wavelength dependence is consistent with those obtained with the Mauna Kea Observatory photometric system employed in the Simultaneous 3-color InfraRed Imager for Unbiased Survey camera attached to the Infrared Survey Facility telescope in previous studies. Such a steep decline of extinction toward the longer wavelengths is also in line with recent results based on deep imaging surveys. The determined extinction law seems to be variable in the VVV from tile to tile, and it is not clear how much of this is due to real sight line variations and how much is due to observational systematic effects. Thus, there might be room for improvement of the extinction law determination from the existing VVV data, but this steep extinction law tends to locate heavily reddened objects in the Galactic plane more distant from us when their distance moduli are calculated from the observed reddening values.

A near infrared variable star survey in the Magellanic Clouds: The Small Magellanic Cloud data

A very long term near-infrared variable star survey towards the Large and Small Magellanic Clouds was carried out using the 1.4m InfraRed Survey Facility at the South African Astronomical Observatory. This project was initiated in December 2000 in the LMC, and in July 2001 in the SMC. Since then an area of 3 square degrees along the bar in the LMC and an area of 1 square degree in the central part of the SMC have been repeatedly observed. This survey is ongoing, but results obtained with data taken until December 2017 are reported in this paper. Over more than 15 years we have observed the two survey areas more than one hundred times. This is the first survey that provides near-infrared time-series data with such a long time baseline and on such a large scale. This paper describes the observations in the SMC and publishes a point source photometric catalogue, a variable source catalogue, and time-series data.

A remarkable oxygen-rich asymptotic giant branch variable in the Sagittarius Dwarf Irregular Galaxy

We report and discuss JHKs photometry for Sgr dIG, a very metal-deficient galaxy in the Local Group, obtained over 3.5 years with the Infrared Survey Facility in South Africa. Three large amplitude asymptotic giant branch variables are identified. One is an oxygen-rich star that has a pulsation period of 950 days, that was until recently undergoing hot bottom burning, with Mbol~-6.7. It is surprising to find a variable of this sort in Sgr dIG, given their rarity in other dwarf irregulars. Despite its long period the star is relatively blue and is fainter, at all wavelengths shorter than 4.5microns, than anticipated from period-luminosity relations that describe hot bottom burning stars. A comparison with models suggests it had a main sequence mass Mi~5 times solar and that it is now near the end of its AGB evolution. The other two periodic variables are carbon stars with periods of 670 and 503 days (Mbol~-5.7 and -5.3). They are very similar to other such stars found on the AGB of metal deficient Local Group Galaxies and a comparison with models suggests Mi~3 times solar. We compare the number of AGB variables in Sgr dIG to those in NGC6822 and IC1613, and suggest that the differences may be due to the high specific star formation rate and low metallicity of Sgr dIG.

Near-infrared Polarimetric Study of the N159/N160 Star-forming Complex in the Large Magellanic Cloud

Abstract We present near-infrared polarimetric results for the N159/N160 star-forming complex in the Large Magellanic Cloud with SIRPOL, the polarimeter of the Infrared Survey Facility. We separated foreground sources using their visual extinction derived from near-infrared photometric data. The 45 young stellar candidates and 2 high-excitation blobs were matched with our sources, and 12 of them showed high polarization that did not originate from the interstellar dust. We made a polarimetric catalog of 252, 277, and 89 sources at the J, H, and K s bands, respectively. Based on the ratios of the polarization degree between these bands, we verify that the origin of these polarized sources is the dichroic extinction from the interstellar dust aligned by the magnetic field and that the ratios follow a power-law dependence of ∼ . The linear polarization vectors projected onto the Hα image of the complex turned out to follow the local magnetic field structure. The vector map overlaid on dust and gas emissions shows the close correlation between the magnetic field structure and surrounding interstellar medium. We suggest that the derived magnetic field structure supports the sequential formation scenario of the complex.

NIR Tully–Fisher in the Zone of Avoidance – III. Deep NIR catalogue of the HIZOA galaxies

We present a deep near-infrared (NIR) photometric catalogue of sources from the Parkes HI Zone of Avoidance (HIZOA) survey, which forms the basis for an investigation of the matter distribution in the Zone of Avoidance. Observations were conducted between 2006 and 2013 using the Infrared Survey Facility (IRSF), a 1.4-m telescope situated at the South African Astronomical Observatory site in Sutherland. The images cover all 1108 HIZOA detections and yield 915 galaxies. An additional 105 bright 2MASS galaxies in the southern ZOA were imaged with the IRSF, resulting in 129 galaxies. The average $K_s$-band seeing and sky background for the survey are 1.38 arcsec and 20.1 mag, respectively. The detection rate as a function of stellar density and dust extinction is found to depend mainly on the HI mass of the HI detected galaxies, which in principal correlates with the NIR brightness of the spiral galaxies. The measured isophotal magnitudes are of sufficient accuracy (errors $\sim$ 0.02 mag) to be used in a Tully-Fisher analysis. In the final NIR catalogue, 285 galaxies have both IRSF and 2MASS photometry (180 HIZOA plus 105 bright 2MASX galaxies). The $K_s$-band isophotal magnitudes presented in this paper agree, within the uncertainties, with those reported in the 2MASX catalogue. Another 30 galaxies, from the HIZOA northern extension, are also covered by UKIDSS Galactic Plane Survey (GPS) images, which are one magnitude deeper than our IRSF images. A modified version of our photometry pipeline was used to derive the photometric parameters of these UKIDSS galaxies. Good agreement was found between the respective $K_s$-band isophotal magnitudes. These comparisons confirm the robustness of the isophotal parameters and demonstrate that the IRSF images do not suffer from foreground contamination, after star removal, nor under-estimate the isophotal fluxes of ZoA galaxies.

Near IR observations of η Car: Reaching its critical rotation?

We report a preliminary result in the monitoring of η Carinae in JHKs bands through the “spectroscopic” event of 2014.5 at InfraRed Survey Facility (IRSF) located in South African Astronomical Observatory (SAAO). The latest photometric data, combined with the data taken with the MK-II photometer [1], show a sign of the same cyclic variation in the J-H vs. H-K diagram reported by Mehner et al.[2]. The change can still be attributed to an apparent increase in black-body temperature, potentially reaching 3,000 to 6,000K as of March 2015.

NEAR-INFRARED POLARIZATION SOURCE CATALOG OF THE NORTHEASTERN REGIONS OF THE LARGE MAGELLANIC CLOUD

ABSTRACT We present a near-infrared band-merged photometric and polarimetric catalog for the 39′ × 69′ fields in the northeastern part of the Large Magellanic Cloud (LMC), which were observed using SIRPOL, an imaging polarimeter of the InfraRed Survey Facility. This catalog lists 1858 sources brighter than 14 mag in the H band with a polarization signal-to-noise ratio greater than three in the J, H, or K s bands. Based on the relationship between the extinction and the polarization degree, we argue that the polarization mostly arises from dichroic extinctions caused by local interstellar dust in the LMC. This catalog allows us to map polarization structures to examine the global geometry of the local magnetic field, and to show a statistical analysis of the polarization of each field to understand its polarization properties. In the selected fields with coherent polarization position angles, we estimate magnetic field strengths in the range of 3−25 μG using the Chandrasekhar–Fermi method. This implies the presence of large-scale magnetic fields on a scale of around 100 parsecs. When comparing mid- and far-infrared dust emission maps, we confirmed that the polarization patterns are well aligned with molecular clouds around the star-forming regions.

Two fast X-ray transients in archival Chandra data

We present the discovery of two new X-ray transients in archival Chandra data. The first transient, XRT 110103, occurred in 2011 January and shows a sharp rise of at least three orders of magnitude in count rate in less than 10 s, a flat peak for about 20 s and decays by two orders of magnitude in the next 60 s. We find no optical or infrared counterpart to this event in pre-existing survey data or in an observation taken by the Simultaneous-3color InfraRed Imager for Unbiased Survey (SIRIUS) instrument at the Infrared Survey Facility ∼2.1 yr after the transient, providing limiting magnitudes of J > 18.1, H > 17.6 and Ks > 16.3. This event shows similarities to the transient previously reported in Jonker et al. which was interpreted as the possible tidal disruption of a white dwarf by an intermediate-mass black hole. We discuss the possibility that these transients originate from the same type of event. If we assume these events are related a rough estimate of the rates gives 1.4 × 105 per year over the whole sky with a peak 0.3–7 keV X-ray flux greater than 2 × 10−10 erg cm−2 s−1. The second transient, XRT 120830, occurred in 2012 August and shows a rise of at least three orders of magnitude in count rate and a subsequent decay of around one order of magnitude all within 10 s, followed by a slower quasi-exponential decay over the remaining 30 ks of the observation. We detect a likely infrared counterpart with magnitudes J = 16.70 ± 0.06, H = 15.92 ± 0.04 and Ks = 15.37 ± 0.06 which shows an average proper motion of 74 ± 19 mas yr−1 compared to archival 2MASS observations. The JHKs magnitudes, proper motion and X-ray flux of XRT 120830 are consistent with a bright flare from a nearby late M or early L dwarf.

Study of morphology and stellar content of the Galactic H ii region IRAS 16148−5011

An investigation of the IRAS 16148−5011 region – a cluster at a distance of 3.6 kpc – is presented here, carried out using multiwavelength data in near-infrared (NIR) from the 1.4 m Infrared Survey Facility telescope, mid-infrared (MIR) from the archival Spitzer GLIMPSE (Galactic Legacy Infrared Midplane Survey Extraordinaire) survey, far-infrared (FIR) from the Herschel archive, and low-frequency radio continuum observations at 1280 and 843 MHz from the Giant Metrewave Radio Telescope and Molonglo Survey archive, respectively. A combination of NIR and MIR data is used to identify 7 Class I and 133 Class II sources in the region. Spectral energy distribution (SED) analysis of selected sources reveals a 9.6 M⊙ high-mass source embedded in nebulosity. However, Lyman continuum luminosity calculation using radio emission – which shows a compact H ii region – indicates the spectral type of the ionizing source to be earlier than B0-O9.5. Free–free emission SED modelling yields the electron density as 138 cm−3, and thus the mass of the ionized hydrogen as ∼16.4 M⊙. Thermal dust emission modelling, using the FIR data from Herschel and performing modified blackbody fits, helped us construct the temperature and column density maps of the region, which show peak values of 30 K and 3.3 × 1022 cm−2, respectively. The column density maps reveal an AV > 20 mag extinction associated with the nebular emission, and weak filamentary structures connecting dense clumps. The clump associated with this IRAS object is found to have dimensions of ∼ 1.1 pc × 0.8 pc, and a mass of 1023 M⊙.

NEAR-INFRARED CIRCULAR POLARIZATION SURVEY IN STAR-FORMING REGIONS: CORRELATIONS AND TRENDS

We have conducted a systematic near-infrared circular polarization (CP) survey in star-forming regions, covering high-mass, intermediate-mass, and low-mass young stellar objects. All the observations were made using the SIRPOL imaging polarimeter on the Infrared Survey Facility 1.4 m telescope at the South African Astronomical Observatory. We present the polarization properties of ten sub-regions in six star-forming regions. The polarization patterns, extents, and maximum degrees of linear and circular polarizations are used to determine the prevalence and origin of CP in the star-forming regions. Our results show that the CP pattern is quadrupolar in general, the CP regions are extensive, up to 0.65 pc, the CP degrees are high, up to 20 %, and the CP degrees decrease systematically from high- to low-mass young stellar objects. The results are consistent with dichroic extinction mechanisms generating the high degrees of CP in star forming regions.

YOUNG STELLAR OBJECT SEARCH TOWARD THE BOUNDARY OF THE CENTRAL MOLECULAR ZONE WITH NEAR-INFRARED POLARIMETRY

We have carried out near-infrared polarimetry toward the boundary of the Central Molecular Zone, in the field of (-1.4 deg $\lesssim l \lesssim$ -0.3 deg and 1.0 deg $\lesssim l \lesssim$ 2.9 deg, $|b|\lesssim$ 0.1 deg), using the near-infrared polarimetric camera SIRPOL on the 1.4 m Infrared Survey Facility telescope. We have selected 112 intrinsically polarized sources on the basis of the estimate of interstellar polarization on Stokes $Q/I-U/I$ planes. The selected sources are brighter than $K_S=14.5$ mag and have polarimetric uncertainty $\delta P<1\,%$. Ten of these distinctive polarized sources are fit well with spectral energy distributions of young stellar objects when using the photometry in the archive of the Spitzer Space Telescope mid-infrared data. However, many sources have spectral energy distributions of normal stars suffering heavy interstellar extinction; these might be stars behind dark clouds. Due to the small number of distinctive polarized sources and candidates of young stellar object, we cannot judge if there is a decline of them outside the Central Molecular Zone. Many of massive candidates of young stellar object in the literature have only small intrinsic polarization. This might suggest that their masses are 4-15 M$_{{\rm sun}}$, whose intrinsic polarization has been expected to be small.

Deep NIR photometry of H i galaxies in the Zone of Avoidance

Current studies of the peculiar velocity flow field in the Local Universe are limited by either the lack of detection or accurate photometry for galaxies at low Galactic latitudes. The contribution to the dynamics of the Local Group of the largely unknown mass distribution in this 'Zone of Avoidance' remains controversial. We present here the results of a pilot project to obtain deep near infrared (NIR) observations of galaxies detected in the systematic Parkes deep HI survey of the ZoA - 578 galaxies with recession velocities out to 6000 km/s were observed with the 1.4m InfraRed Survey Facility SIRIUS camera providing J, H and K_s imaging ~2 mag deeper than 2MASS. After star-subtraction, the resulting isophotal magnitudes and inclinations of ZoA galaxies are of sufficient accuracy (magnitude errors under 0.1 mag even at high extinction) to ultimately be used to determine cosmic flow fields "in" the ZoA via the NIR Tully-Fisher relation. We further used the observed NIR colours to assess the ratio of the true extinction to the DIRBE/IRAS extinction deep into the dust layers of the Milky Way. The derived ratio was found to be 0.87 across the HIZOA survey region with no significant variation with Galactic latitude or longitude. This value is in excellent agreement with the completely independently derived factor of 0.86 by Schlafly & Finkbeiner based on Sloan data far away from the Milky Way.

Star formation activity in the southern Galactic H ii region G351.63−1.25

The southern Galactic high mass star-forming region, G351.6-1.3, is a HII region-molecular cloud complex with a luminosity of 2.0 x 10^5 L_sun, located at a distance of 2.4 kpc. In this paper, we focus on the investigation of the associated HII region, embedded cluster and the interstellar medium in the vicinity of G351.6-1.3. We address the identification of exciting source(s) as well as the census of stellar populations. The ionised gas distribution has been mapped using the Giant Metrewave Radio Telescope (GMRT), India at three continuum frequencies: 1280, 610 and 325 MHz. The HII region shows an elongated morphology and the 1280 MHz map comprises six resolved high density regions encompassed by diffuse emission spanning 1.4 pc x 1.0 pc. The zero age main-sequence (ZAMS) spectral type of the brightest radio core is O7.5. We have carried out near-infrared observations in the JHKs bands using the SIRIUS instrument on the 1.4 m Infrared Survey Facility (IRSF) telescope. The near-infrared images reveal the presence of a cluster embedded in nebulous fan-shaped emission. The log-normal slope of the K-band luminosity function of the embedded cluster is found to be 0.27 +- 0.03 and the fraction of the near-infrared excess stars is estimated to be 43%. These indicate that the age of the cluster is consistent with 1 Myr. The champagne flow model from a flat, thin molecular cloud is used to explain the morphology of radio emission with respect to the millimetre cloud and infrared brightness.